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All questions of Science for Class 10 Exam

Which of the following is a combination reaction?
  • a)
    CaCO3 → CaO + CO2
  • b)
    H2 + Cl2 → 2HCl
  • c)
    H2CO3 → H2O + CO2
  • d)
    2KClO3 → 2KCl + 3O2
Correct answer is option 'B'. Can you explain this answer?

Roshni chauhan answered
Balanced Equation:
H2 + Cl2 → 2HCl2
The above reaction is an example of combination reaction because two different elements are combining to form a single compound.
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Which of the following is a decomposition reaction?
  • a)
    NaOH + HCl → NaCl + H2O
  • b)
    NH4CNO → H2NCONH2
  • c)
    2KClO3 → 2KCl + 3O2
  • d)
    H2 + I2 → 2HI
Correct answer is option 'C'. Can you explain this answer?

Meera Rana answered
A decomposition reaction occurs when one reactant breaks down into two or more products. Examples of decomposition reactions include the breakdown of hydrogen peroxide to water and oxygen, and the breakdown of water to hydrogen and oxygen.
2KClO3 → 2KCl + 3O2

Which of the following does not conduct electricity?
  • a)
    Sodium hydroxide
  • b)
    Rain water
  • c)
    Hydrochloric acid
  • d)
    Distilled water
Correct answer is option 'D'. Can you explain this answer?

Gaurav Kumar answered
Distilled water do not conduct electricity. The reason is that a liquid conducts electricity is by the positively or negatively charged ions that are actually moving from one of the electrodes to the other, carrying charge (electricity) with them.

The reaction C + O2  → CO2 + Heat is a:
  • a)
    Combination reaction
  • b)
    Oxidation reaction
  • c)
    Exothermic reaction
  • d)
    All of the above
Correct answer is option 'D'. Can you explain this answer?

Amit Sharma answered
C + O2  → CO2 + Heat
  • This is a Combination reaction because C and O2 are combining to produce one single compound CO2.
  • This is also an Oxidation reaction because carbon is getting oxidized.
  • This is also an exothermic reaction because in this reaction heat is getting released.
​​​​​​​So Option D is correct

Which one of the following will be required to identify the gas evolved when diluted HCl reacts with zinc metal?
  • a)
    Red litmus solution
  • b)
    Lime water
  • c)
    A burning splinter
  • d)
    Blue litmus solution
Correct answer is option 'C'. Can you explain this answer?

Kiran Mehta answered
A burning splinter since hydrogen gas burns with a pop sound.
Zinc being an active metal readily reacts with hydrochloric acid at room temperature to form soluble zinc chloride and hydrogen.
Zn + 2HCl → ZnCl2 + H2.

To get 2Ω resistance using only 6Ω resistors, the number of them required is
  • a)
    2
  • b)
    3
  • c)
    4
  • d)
    6
Correct answer is option 'B'. Can you explain this answer?

Avinash Patel answered
Three resistors of 2Ω is required to get 6Ω because resultant is more than individual so they all must be connected in series.

The best conductor of electricity among the following is:
  • a)
    Hg (Mercury)
  • b)
    Al (Aluminum)
  • c)
    Ag (Silver)
  • d)
    Au (Gold)
Correct answer is option 'C'. Can you explain this answer?

Avinash Patel answered
Metals are good conductors of electricity. silver is found in in pure form from the earth. so  In the given options all are metals. Among them silver is the best conductor of electricity after second best conductor of electricity is gold.

Metal which is a poor conductor of heat is:
  • a)
    Zinc
  • b)
    Lead
  • c)
    Gold
  • d)
    Copper
Correct answer is option 'B'. Can you explain this answer?

Anjana Khatri answered
Although metals are supposed to be good conductors of electricity and heat,metals like mercury, lead, alloys of iron and chromium, titanium and stainless steel are poor conductors when compared to silver, copper and gold.

Which of the following is a displacement reaction?
  • a)
    CaCO3 → CaO + CO2
  • b)
    CaO + 2HCl → CaCl2 + H2O
  • c)
    Fe + CuSO4 → FeSO4 + Cu
  • d)
    NaOH + HCl → NaCl + H2O
Correct answer is option 'C'. Can you explain this answer?

Gaurav Kumar answered
Fe + CuSo4 → FeSO4 + Cu 
is displacement reaction.
In these reaction iron (Fe) displace copper (Cu) 
Hence, it is a displacement type of reaction.
(a) is a decomposition reaction.
(b) and (d) are neutralisation reactions.

Identify the amphoteric oxide from the following:​
  • a)
    MgO
  • b)
    Na2O
  • c)
    Al2O3
  • d)
    K2O
Correct answer is option 'C'. Can you explain this answer?

Arun Sharma answered
Amphoteric metal oxides react with both acids as well as bases to produce salt and water.
Aluminium oxide is an amphoteric oxide because it reacts with acids as well as bases and form salts and water.
Al2O3     +     6HCl     →     2AlCl3    +    3H2O                      (Basic nature)
Aluminium   Hydrochloric   Aluminium      Water
   oxide            acid          chloride
 
Al2O3        +       2NaOH    →      2NaAlO2     +     H2O           (Acidic nature)
Aluminium           Sodium              Sodium          Water
   oxide             Hydroxide          aluminate        

Identify ‘X’ in the reaction: 2HCl + CuO → X + H2O​
  • a)
    CuCl
  • b)
    Cu(OH)2
  • c)
    CuCl2
  • d)
    HOCl
Correct answer is option 'C'. Can you explain this answer?

Vikram Kapoor answered
When copper oxide and dilute hydrochloric acid are mixed the blue green solution is formed. 
The reaction is :- 
CuO + 2HCl → CuCl2 + H2O

Which of the following metals comes above zinc in reactivity series?
  • a)
    Silver
  • b)
    Copper
  • c)
    Aluminium
  • d)
    Iron
Correct answer is option 'C'. Can you explain this answer?

Karthik murthy answered
Reactivity Series:

The reactivity series is a list of metals arranged in order of their decreasing reactivity. The most reactive metal is placed at the top and the least reactive metal is placed at the bottom of the series.

The reactivity series of metals is as follows:

Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver > Gold

Explanation:

Aluminium is more reactive than zinc and is placed above zinc in the reactivity series. This is because aluminium has a stronger tendency than zinc to lose electrons and form positive ions.

When aluminium is exposed to air, it reacts with oxygen to form a layer of aluminium oxide. This layer of oxide is very thin and is also very stable. It prevents further reaction of aluminium with oxygen and protects the metal from corrosion.

Zinc, on the other hand, reacts with oxygen in the air to form zinc oxide. However, the layer of oxide formed on zinc is not as stable as the layer of oxide formed on aluminium. Therefore, zinc is more susceptible to corrosion than aluminium.

Conclusion:

In conclusion, aluminium is more reactive than zinc and is placed above zinc in the reactivity series. This means that aluminium can displace zinc from its compounds in a chemical reaction, but zinc cannot displace aluminium from its compounds.

All metals exist as solid at room temperature except the metal ‘X’. Name the metal “X’.
  • a)
    Tungsten
  • b)
    Mercury
  • c)
    Gold
  • d)
    Potassium
Correct answer is option 'B'. Can you explain this answer?

Ananya Das answered
It is the only metal that is liquid at room temperature. It has the lowest melting point and boiling point of any other metal. It has low thermal conductivity, and a quite low electrical conductivity. It is the only metal that doesn’t form diatomic molecules in the gaseous phase.

The colour of phenolphthalein in acids is:
  • a)
    Colourless
  • b)
    Red
  • c)
    Pink
  • d)
    Blue
Correct answer is option 'A'. Can you explain this answer?

Krishna Iyer answered
Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colourless in acidic solutions and magenta in basic solutions.

The magnetic field lines inside a long current-carrying solenoid are near-

  • a)
    Straight
  • b)
    Circular
  • c)
    Elliptical
  • d)
    Parabolic
Correct answer is option 'A'. Can you explain this answer?

Gunjan Lakhani answered
The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.

Carbon dioxide is an example of:
  • a)
    Amphoteric oxide
  • b)
    Acidic oxide
  • c)
    Basic oxide
  • d)
    Neutral oxide
Correct answer is option 'B'. Can you explain this answer?

Gaurav Kumar answered
Acid oxides is a complex chemical substance oxides, which form a salt with the chemical reactions with bases or basic oxides and do not react with acidic oxides.
Examples of acidic oxides can be:
CO2 (all known carbon dioxide), P2O5 - oxide of phosphorus (formed in air if burns white phosphorus), SO3 - oxide of sulfur (VI) is a substance used for sulfuric acid.

The reaction H2 + Cl2 → 2HCl is a –
  • a)
    Decomposition reaction
  • b)
    Combination reaction
  • c)
    Double displacement reaction
  • d)
    Displacement reaction
Correct answer is option 'B'. Can you explain this answer?

Anjana Khatri answered
It is a reaction in which two substances react with each other to make a single substance. Therefore, H2 + CL2 = 2HCL is an COMBINATION REACTION. It is a special case of addition reaction known as synthesis.

Transparent medium is one :
  • a)
    Which allows light to pass through
  • b)
    Which absorbs most of the light
  • c)
    Which do not allows light to pass through
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Imk Pathshala answered
A transparent medium is a material that partially allows light to pass through.
When light encounters a transparent medium, it can penetrate the material and transmit through it.
Examples of transparent mediums include glass, water, and air.
Transparent mediums are essential for various applications such as optics, windows, and lenses.

     
 

In reaction SO2 + 2H2S → 2H2O + 3S, the reducing agent is
  • a)
    SO2
  • b)
    H2S
  • c)
    H2O
  • d)
    S
Correct answer is option 'B'. Can you explain this answer?

Raghav Bansal answered
  • In the reaction SO2 is getting reduced to S as oxygen is being removed.
  • Similarly, H2S is oxidised to S as hydrogen is removed.
  • The species getting oxidised facilitates the reduction process and is the reducing agent.
  • Hence, H2S is the reducing agent and Oxidising agent is SO2.
So, option B is correct

The Law of Octaves was applicable only upto element ________.
  • a)
    Sodium
  • b)
    Calcium
  • c)
    Zinc
  • d)
    Copper
Correct answer is option 'B'. Can you explain this answer?

Vikram Kapoor answered
The major limitations of Newlands' law of octaves were : 
It was applicable to only lighter elements having atomic masses upto 40 u, i.e., upto calcium. After calcium, the first and the eighth element did not have similar properties. For example chromium (Cr) and yttrium (Y) are the first and the eighth element placed in the same column but they have entirely different properties.  

Magnetic lines of force originate from the
  • a)
    North pole
  • b)
    Center point
  • c)
    South pole
  • d)
    Either north pole or south pole
Correct answer is option 'A'. Can you explain this answer?

Ananya Das answered
The direction of magnetic line of force is the direction of force on a North Pole, so the magnetic lines of force always begin on the North Pole of a magnet and end on the South Pole of the magnet. When a small magnetic compass is placed along a lie of force, it sets itself along the line tangential to it. Hence, the line drawn from the South Pole of the compass to its North pole shows the direction of the magnetic field.

Which of the following non-metal is good conductor of electricity?
  • a)
    Graphite
  • b)
    Phosphorus
  • c)
    Hydrogen
  • d)
    Bromine
Correct answer is option 'A'. Can you explain this answer?

Gaurav Kumar answered
Carbon, in the form of Graphite is a good conductor of electricity. It conducts heat and electricity like a metal or a metalloid.

Can you explain the answer of this question below:

Haemoglobin is –

  • A:

    Vitamin

  • B:

    Skin pigment

  • C:

    Blood carrier

  • D:

    Respiratory pigment

The answer is D.

Krishna Iyer answered
the hemoglobin increases the oxygen carrying capacity of blood. In humans and most other vertebrates, the most common respiratory pigment is a protein called hemoglobin.

Asexual reproduction is good because it:
  • a)
    Involves two parents
  • b)
    Is simple and fast
  • c)
    Shows no variation
  • d)
    Produces defect in offspring
Correct answer is option 'B'. Can you explain this answer?

Anjana Khatri answered
Asexual reproduction occurs when an organism makes more of itself without exchanging genetic information with another organism through sex.In sexually reproducing organisms, the genomes of two parents are combined to create offspring with unique genetic profiles. This is beneficial to the population because genetically diverse populations have a higher chance of withstanding survival challenges such as disease and environmental changes.

Asexually reproducing organisms can suffer a dangerous lack of diversity – but they can also reproduce faster than sexually reproducing organisms, and a single individual can found a new population without the need for a mate.

Identify the type of reaction: HCl + NaOH → NaCl + H2O
  • a)
    Combination reaction
  • b)
    Double decomposition reaction
  • c)
    Decomposition reaction
  • d)
    Neutralisation reaction
Correct answer is option 'D'. Can you explain this answer?

Krishna Iyer answered
Reaction of a strong acid with strong base is called neutralization reaction which produces salt and water,
HCl + NaOH → NaCl + H2O
This equation is already balanced.

Ability of the eye to see objects at all distances is called
a)Binocular vision
b)Myopia
c)Accommodation
d)Hypermetropia
Correct answer is option 'C'. Can you explain this answer?

Ishan Choudhury answered
Changes in the contraction of the ciliary muscles alter the focal distance of the eye, causing nearer or future images to come into focus on the retina; this process is known as accommodation.

Which part of seed on germination develops into shoot?
  • a)
    Funicle
  • b)
    Cotyledon
  • c)
    Radicle
  • d)
    Plumule
Correct answer is option 'D'. Can you explain this answer?

Rahul Kapoor answered
In plant physiology, the epicotyl is the embryonic shoot above the cotyledons. In most plants theepicotyl will eventually develop into the leaves of the plant. In dicots, the hypocotyl is what appears to be the base stem under the spent withered cotyledons, and the shoot just above that is theepicotyl.
Which is commonly called as plumule , which forms shoot parts And radicle forms root parts.

If four resistors each of 1Ω are connected in parallel, the effective resistance will be
  • a)
    0.5Ω
  • b)
    0.25Ω
  • c)
    4Ω
  • d)
    2Ω
Correct answer is option 'B'. Can you explain this answer?

Gaurav Kumar answered
If four resistors each of 1Ω are connected in parallel, the effective resistance will be 0.25Ω..
As, in parralel connection,
1/Reff. = 1/R1 + 1/R2 + ....

A lustrous non-metal is:
  • a)
    Iodine
  • b)
    Bromine
  • c)
    Chlorine
  • d)
    Sulphur
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
Non - metals do not have luster. They do not reflect light from their surface ( except iodine and diamond) . So, here a lustrous now Metal is iodine.

The human eye forms the image of an object at its
  • a)
    Iris
  • b)
    Pupil
  • c)
    Cornea
  • d)
    Retina
Correct answer is option 'D'. Can you explain this answer?

Rahul Kapoor answered
Retina is the inner back portion of eye. Retina is composed of enormous number of light sensitive cells. Lens forms image of the visual world on retina through cornea. Light sensitive cells of retina get activated upon illumination and generate electric signals. Optic nerves send these electric signals to the brain, where these signals finally processed and interpreted to see an object as they are.

The lustre of a metal is due to:
  • a)
    Its high density
  • b)
    Presence of free electrons
  • c)
    Its high polishing
  • d)
    Its chemical inertness
Correct answer is option 'B'. Can you explain this answer?

Rohini Seth answered
The lustre of a metal is due to presence of free electrons.
It has to do with the way light and electrons on the surface of metals interact. The outer electrons in a metal are almost not bound to any individual atom, thus are relatively free, and are concentrated on the surface. These electrons (electron density) tend to oscillate at a collective frequency. 

The colour of zinc metal is
  • a)
    reddish-brown
  • b)
    grey 
  • c)
    Blue
  • d)
    silvery-white
Correct answer is option 'D'. Can you explain this answer?

Vikas Kumar answered
The correct option is D
silvery-white
Explanation for correct option
(D) The color of Zinc metal is silvery.
  • An electron gets excited to a higher energy orbital from a lower energy d orbital. The frequency of light absorbed is proportional to the excitation energy.
  • This frequency is usually in the visible range.
  • The color seen corresponds to the complementary color of the light absorbed.
  • Zinc (Zn) is a silvery-white metal.
Hence, option (D) is correct. The color of Zinc metal is silvery.

Which of the following has the maximum non-metallic character ?
  • a)
    F
  • b)
    Cl
  • c)
    Br
  • d)
    I
Correct answer is option 'A'. Can you explain this answer?

Ananya Das answered
Non metallic character decreases as we move down the group. In a group, the size of an element increases because there is an addition of new shell and electron  is added in that shell. Hence, fluorine has the most non metallic character. 

Which of the following is not an example of chemical change?
  • a)
    rusting of iron
  • b)
    milk changes to curd
  • c)
    digestion of food in our body
  • d)
    changing of water to water vapour
Correct answer is option 'D'. Can you explain this answer?

Amit Sharma answered
The process of changing water vapour into water is called condensation. It is not a chemical reaction.
When milk converts in curd the process is irreversible and a new substance with different properties is formed hence it is an example of a chemical change.
Rusting of iron is also a chemical change.
 

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