Chemistry Mock Test- 1 - Class 9 MCQ

Atomic mass of Sulphur is 32 u and atomic mass of Carbon is 12 u. So, mass of Sulphur is 32/12 times heavier than Oxygen. = 8/3 times.

Naphthalene undergoes sublimation easily i.e., the change of state of naphthalene from solid to gas without the intervention of the liquid state. Thus, naphthalene balls keep on forming naphthalene vapours which disappear into the air with time without leaving any solid.

Diffusion becomes faster at high temperatures. This is because, at higher temperatures, the particles of matter gain more kinetic energy, allowing them to move more rapidly and intermix more quickly. As temperature increases, the kinetic energy overcomes the forces of attraction between particles, facilitating faster diffusion.

The random movement of microscopic particles in a fluid is known as Brownian motion. This phenomenon was first observed by Robert Brown and is a result of continuous collisions between the particles and molecules in the surrounding medium.

Higher the melting point of a substance, greater will be the force of attraction between particles. The melting point of iron is considerably high, so the force of attraction between its particles is higher.

The fourth shell of an atom can hold a maximum of 32 electrons, depending on the element. There are four subshells - 4s, 4p, 4d, and 4f - that can hold a maximum of 2, 6, 10, and 14 electrons, respectively, for a total of 32.

The maximum number of electrons present in a shell = 2n2

 

Where n = shell number

Value of n for K shell = 1

Therefore, Maximum number of electrons in K shell = 2n2 = 2(1) = 2

Value of n for L shell = 2

Therefore, Maximum number of electrons in L shell = 2(2)2 = 8

Thus, total no. of electrons = 2 + 8 = 10

Definition of a mole:
- The correct definition of a mole is option B: It contains 6.022×10^23 atoms of a given substance.
Explanation:
- The mole is a unit of measurement used in chemistry to represent a specific amount of a substance.
- It is defined as the amount of a substance that contains the same number of entities (atoms, molecules, ions, etc.) as there are atoms in 12 grams of carbon-12.
- The number of entities in a mole is known as Avogadro's number, which is approximately 6.022×10^23.
- Therefore, a mole represents a specific quantity of a substance, regardless of its atomic or molecular mass.
- The correct definition of a mole is that it contains 6.022×10^23 atoms of a given substance, as stated in option B.
Incorrect options:
A. It is equal to the gram atomic mass of the substance:
- This is not the correct definition of a mole. The gram atomic mass is the mass of one mole of atoms of an element, but it does not define what a mole is.
C. It is equal to the gram molecular mass of the substance:
- This is not the correct definition of a mole. The gram molecular mass is the mass of one mole of molecules of a compound, but it does not define what a mole is.
D. It contains 6.022×10^23 molecules of a given substance:
- This statement is incorrect because a mole can contain atoms, molecules, ions, or any other entities, not just molecules.

An element is a simple substance that cannot be broken down into simpler substances. There are more than 100 elements found on Earth. Eg., oxygen, hydrogen, gold, silver, etc.

Bohr first made use of quantum theory to explain the structure of atom and proposed that energy of electron in an atom is quantized

Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus.

Humidity refers to presence of vapour in air. So, if humidity increases then the rate of evaporation decreases as vapours in air are already present.

Cesium is a metal which has very low melting point and change into liquid state above  30⁰C.

Elements Used in Radiation Therapy. Radiation therapy is an important cancer treatment along with chemotherapy and surgery. The most famous type is probably gamma ray irradiation by radioactive cobalt-60.

Atoms of the same element having the same atomic numbers but different mass numbers are termed as isotopes.

Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.

Average atomic mass of chlorine is given by:

(35 x 3) + (37 x 1)/4 = 35.50 u

Kinetic Molecular Theory states that gas particles are in constant motion and exhibit perfectly elastic collisions. Kinetic Molecular Theory can be used to explain both Charles' and Boyle's Laws. The average kinetic energy of a collection of gas particles is directly proportional to absolute temperature only.

Molar mass of sucrose = 342 g
No. of Oxygen atoms in 3.42g of (C₁₂H₂₂O₁₁) = 11 x NA
Therefore, No. of Oxygen atoms in 342g of (C₁₂H₂₂O₁₁) = 11 x Na x 3.42 / 342
= 0.11 NA
No. of oxygen atoms in 18g of H₂O = 1NA 
Therefore, Total no. of Oxygen atom in 342g of Sucrose and 18g of water 
= 0.11NA +1NA = 1.11NA = 1.11 x 6.02 x 10²³ ⇒ 6.68 * 10²³

As from law of conservation of mass:-mass of reactants=mass of product Therefore, mass of compound A + mass of compound B=mass of compound C So, 5g + 10g= 15g

Correct answer is A. 
Evaporation occurs at the surface of a liquid because the particles at the surface have sufficient energy to break through the forces of attraction between them.

An oxygen molecule (O2) is a good example of a molecule with a covalent bond. Ionic bonds occur when electrons are donated from one atom to another. Table salt (NaCl) is a common example of a compound with an ionic bond.

e correct answer is c

   The process by which we can separate the particles of a colloidal solution is called Centrifugation.

In Kelvin temperature, the symbol (^∘) is not used. Mercury is used in glass thermometers because it does not stick with glass and have shiny surface to viewed easily.

Dalton’s Atomic Theory was given by John Dalton.
According to this theory: -
(a) Matter is made up of invisible particles known as atoms.
(b) The properties of all the atoms of a given element are the same including mass.
(c) Atoms of different elements combine in fixed ratios to form compounds.
(d) Atoms are neither created nor destroyed.
(e) The formation of new products results from the rearrangements of existing atoms.
(f) Atoms of an element are identical in mass, size and properties.

The correct option is D.
The atomic size is of the order of 10⁻⁸
cm or 10⁻¹⁰ m or one angstrom unit.
On the other hand, the radius of an atomic nucleus is of the order of 10⁻¹³
cm or 10⁻¹⁵ m or one Fermi unit.

Isotopes are the atoms of the same element with similar atomic number but different atomic mass.The elements of isotopes share same chemical properties but different physical properties

At 50°C water will be in its liquid state.