Test : Atoms And Molecules- 2


20 Questions MCQ Test Science & Technology for UPSC CSE | Test : Atoms And Molecules- 2


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QUESTION: 1

Which one of the following phrases would be incorrect to use?

Solution:

 it  will be incorrect to say that  an  atom of  a compound   because, 
Every combination of atoms is a molecule. A compound is a molecule made of atoms  from different elements. All compounds are molecules , but not all molecules are compounds.

QUESTION: 2

Which of the following illustrates the law of conservation of mass?

Solution:

Correct Answer :- b

Explanation : According to the statement following reaction takes place-

AgNO3 + HCl → AgCl + HNO3

Now according to the law,

Mass of reactants (AgNO3 + HCl) = Mass of products (AgCl + HNO3)

Total mass of reactants = 1.70 + (100×0.1×10-3×36.5) = 2.065g

Total mass of products = 0.63 + 1.435 = 2.065 g

QUESTION: 3

The law of constant proportion was proposed by

Solution:

In 1806, Proust summarized his observations in what is now called Proust's Law. It stated that chemical compounds are formed of constant and defined ratios of elements, as determined by mass. For example, carbon dioxide is composed of one carbon atom and two oxygen atoms.

QUESTION: 4

A compound contains 8% sulphur by mass. The minimum molecular weight of the compound is:

Solution:

The compound Sulphur = 8%
Therefore, 8g of S is present in 100g.
(Least molecular mass means that at least one atom of Sulphur should be present in a molecule.)
Therefore, 32g of S is peasant in 100/8 x 32 = 400

QUESTION: 5

The mass of one atom of carbon-12 is

Solution:

Mass of one atom = Avogadro′s numberMass of one mole of atom​=12/6.02×1023

Mass of one carbon atom = 1.994×10−23g

QUESTION: 6

Identify the correct one from the following statements. 

Solution:

option ( c) The mixture has properties similar to its compound is the correct answer. 

 

Explanation:- 

This is because in a mixture, the constituent particles are not mixed chemically.
They are mixed physically and can be separated fairly easily by physical Methods.
Thus they show the properties of components.
Example can be alloys.

QUESTION: 7

The atom is indivisible, was proposed by

Solution:
QUESTION: 8

18 g of water is electrolysed. The weight of oxygen formed will be 

Solution:
QUESTION: 9

Modern atomic symbols are based on the method proposed by

Solution:
QUESTION: 10

The balancing of chemical equation is based on 

Solution:
QUESTION: 11

Which of the following is the chemical symbol for nitrogen gas?

Solution:

Nis the chemical symbol for nitrogen gas.

QUESTION: 12

Which of the following is correct statement ?

Solution:
QUESTION: 13

Latin name for iron is

Solution:
QUESTION: 14

Molecular weight of CuS04. 5H20 is equal to 
[Cu = 63.5 u, S = 32 u, O — 16 u, H = 1 u]

Solution:
QUESTION: 15

Which of the following represents a correct chemical formula?

Solution:
QUESTION: 16

How many moles of electrons weigh equal to one kilogram? [Mass of 1 e = 9.1 x 10-31 kg]

Solution:
QUESTION: 17

3.42 g sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are

Solution:

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

QUESTION: 18

Arrange the following in increasing order of number of molecules. 
I. 0.5 mol of H2 
II. 4.0 g of H2 
III. 18 g of H2
IV 2.2 g of CO2 

Solution:

option ( b) is the correct✔ answer. 

 

Explanation:- first we have to calculate, the no. of molecules  and then we will compare them. To calculate the number of molecules, we multiply no. of moles with the Avagadro's number. 

  • 0.5 *( 6.022 * 10^23) 

=  3.11 * 10^ 23

  • 2* ( 6.022 * 10^23) 

=  12.044 * 10^ 23

  • 3.35 * 10^19

  • 0.05 * ( 6.022 * 10^23) 

= 0.3011 * 10^ 23


So, we can see, 4<1<3<2   is the correct✔ answer.

QUESTION: 19

Which of the following symbols is incorrect?
(i) Helium (He)
(ii) Aluminium (AL)
(iii) Carbon (c)
(iv) Cobalt (CO)
Select the correct alternative:

Solution:

Because , the symbol used for aluminum is Al,  the symbol used for carbon is C,  the symbol used for cobalt is Co.

QUESTION: 20

The mass of sodium in 5.85 g of NaCl is 

Solution:

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