# Atoms and Molecules Viva Questions

**ATOMS AND MOLECULES
VIVA QUESTIONS (CLASS 9)**

1. What is the Avogadro number of Helium (He) atoms weigh ?

**Ans: 4.0 g **

2.
Determine the number of hydrogen atoms in 3 mole of NH_{3} ?

**Ans: 9 x 6.02 x 10 ^{23}
**

3.
Which of the following weighs least among
the following?

(a)
0.224 litres of O_{2} at NTP

(b)
6.02 x 10^{23} molecules of oxygen

(c) 6.02 x 10^{23} atoms of carbon

(d)
10 g of CO2

**Ans: 0.224 litres of O _{2}
at NTP**

4.
An element's oxides contain 57.1 % and 72.1 % oxygen, respectively. What is the
second oxide if the first oxide is MO?

**Ans: MO _{2}**

5. What is the molarity of Na_{2}CO_{3}
solution containing 10.6 g per 500 ml solution?

**Ans: 0.2 **

6.
Determine the volume of 0.5 M HNO_{3} that can be prepared from 25 mL
of 2.5 M HNO_{3} ?

**Ans: 125 mL**

7.
If 30 L is converted into SI unit and expressed in scientific notation, determine the value obtained?

**Ans: 3 x 10 ^{-2} m^{3} **

8.
The average density of earth is 5.5 g cm^{-3}. In kg m^{-3}, determine
the average density?

**Ans: 5.5 x 10 ^{-3}
**

9.
In 1.0046, how many significant figures
are there?

**Ans: five **

10.
From the given lists, which of the following has more number of rnolecules ?

(a)
1 g CO_{2}

(b)
1 g N_{2}

(c)
1 g H_{2}

(d)
1 g CH_{4}

**Ans: 1 g H _{2}**

11.
Carbon monoxide and carbon dioxide may be taken as examples for illustrating which
law ?

**Ans: Law of multiple
proportions **

12.
From the given, which of the following contains Avogadro number of atoms,

(a)
11.2 L of H_{2} at STP

(b) 32 g of oxygen

(c)
28 g nitrogen

(d) 22.4 L of Cl_{2} at STP

**Ans: 11.2 L of H _{2}
at STP**

13.
Find the volume of oxygen at STP required to react with 3 g graphite to give CO_{2}
?

**Ans: 5.6 L**

14.
A solute has a molecular mass of 60 g and 90 g of it is dissolved in a litre of
solution. Then what is its molarity?

**Ans: 1.5**

15. From the given samples, determine which of
the following is not a mixture?

(a) air (b) milk (c) smoke (d) water

**Ans: Water**

16.
The volume of l g of a gas at STP is 1.12 L. What will be its molecular mass ?

**Ans: 20 **

17. A mass of 16 g of an element was mixed
with 32 g oxygen when 32 g of compound was formed. If the element was the
limiting reagent, what will be the mass ratio of the element to oxygen in the
compound ?

**Ans: 1:1 **

18.
Chemical equations are balanced so that they are in accordance with which law?

**Ans: Law of
conservation of mass **

19.
At NTP, 0.225 g of carbon reacts with 140 mL of oxygen. What would the
compound's molecular formula be then?

**Ans: C _{3}O_{2}
**

20.
0.25 g of a tetratomic element is 3.125 x 10^{-3} mole. Then what is the
atomic mass of the element is

**Ans: 20**

21.
Neon contains two isotopes of atomic masses 20 and 22 in the mass ratio 9 : 1 respectively. Find the atomic mass of the
element ?

**Ans: 20.2**

22.
What is the atomicity of ozone?

**Ans: The atomicity of
ozone is 2**

23. Determine which molecule from the
following elements is tetratomic?

(a) ozone (b) phosphorus (c) sulphur (d) xenon

**Ans: Phosphorus**

24.
What is the number of significant figures in 6.023 x 10^{23} ?

**Ans: The number of
significant figures is 4 **

25.
Determine the approximate number of atoms present in lg CH_{3}COOH ?

**Ans: The approximate number of atoms present is 10 ^{22
}**

26.
Find the number of significant figures in 0.0480 ?

**Ans: The number of
significant figures is 3**

27.
Give the number of dimensionally independent physical quantities in SI units?

**Ans: 7**

28.
Give the equivalent of 1 cm^{3} of volume?

**Ans: 10 ^{-3} dm^{3}**

29.
Determine the equivalent of one joule of energy ?

**Ans: 0.2381 cal **

30.
From the following, determine the SI unit of work?

(a) cal (b) Joule (c) litre-atm (d) ergs

**Ans: Joule**

31.
One kg weight is equivalent to

**Ans: 9.8 N **

32.
The unit of J. Pa^{-I} is equivalent to

**Ans: m ^{3} **

33.
From the listed elements, determine which
of the element is not an element?

(a) Diamond (b) 22 carat gold (c) graphite (d)
oxygen

**Ans: 22 carat gold**

34.
From the given mixtures, find which one
is not a homogeneous mixture?

(a)
one rupee coin (b) gasoline (c) iodised table salt (d) air

**Ans: Iodised table salt**

35.
Give the mass of a Mg atom ?

**Ans: The mass of Mg
atom is 24.3/6.02 x 10 ^{23} g **

36.
Determine the number of mols of carbon
present in 1 mot of ethanol?

**Ans: 2 **

37.
615.00 has...........significant figures

**Ans: 5**

38.
How will you measure the Luminous intensity ?

**Ans: The luminous
intensity is measured in terms of Candela **

39.
The prefix tera means

**Ans: 10 ^{12 }**

40.
Pure water can be obtained from sea water by which process?

**Ans: Distillation process**

41.
From the listed elements, find which one contains the largest number of
molecules?

(a)
1g CO_{2} (b) 1g N_{2} (c)
1 g H_{2} (d) 1 g CH_{4 }

**Ans: 1 g H _{2} **

42.
Carbon forms two oxides CO and CO_{2}. This illustrates which law?

**Ans: Law of Multiple proportions **

43.
Two oxides of a metal contain 50% and 60% of oxygen respectively. If the formula
of the first oxide is MO, determine the formula of the second one?

**Ans: The formula of the
second one is M _{2}O_{3} **

44.
What is the simplest formula for a compound with 50% of element X (atomic mass
10) and 50% of element Y (atomic mass 20) in it?

**Ans: The simplest
formula is: X _{2}Y**

45.
Which of the following contains the same number of atoms as in 6 g carbon?

(a)
24 g Mg (b) 23 g Sodium (c) 20 g Ca
(d) 63.5 g Cu

**Ans: 20 g Ca **

46.
3.2 g of gas contains 6.02 x 10^{22} molecules. determine its vapour
density?

**Ans: The vapour density
is 16**

47.
Find the volume of 1 M NaOH required to convert 1.2 g of NaHSO_{4}
completely to Na_{2}SO_{4} ?

**Ans: 10 ml**

48.
How many moles of water would be formed when 4 g of methane (CH_{4})
are burnt?

**Ans: 0.5**

49.
calculate the number of significant figures of the following numbers?

(a)
100.04

**Ans: 5**

(b)
4.20 x 10^{10}** **

**Ans: 3**

(c)
324.0

**Ans: 4**

(d)
500.00

**Ans: 5**

(e)
0.02670

**Ans: 4**

50.
Compute the following:

(a)
5.28 x 0.156 x 3/0.428

**Ans: 5.77**

(b)
5.28 x 0.156 x 3/0.421

**Ans: 5.67**

51.
List the proper number of significant
figures in the following and indicate which zeros are significant?

(a)
0.216

**Ans: 3 Significant
figures**

(b)
90.1

**Ans: 3 Significant
figures and zero is significant**

(c)
800.0

**Ans: 4 Significant
figures all zeros are significant**

(d)
0.0670

**Ans: 3 Significant
figures, last zero is significant**

52. Determine the number of moles of Oxygen atoms
are there in

(a)
one mole of HNO_{3}

**Ans: 3 moles**

(b)
one mole of H_{2}SO_{4 }

**Ans: 4 moles**

53.
Determine the number of moles of water produced when 8 g of methane (CH_{4})
are burnt?

**Ans: 1 mol.**

54.
How many moles of KClO_{3} are needed to give 1.5 moles of oxygen?

**Ans: 1 mol.**

55.
How many moles of KCl are formed when 0.33 mol of KClO_{3 }is
decomposed?

**Ans: 0.33 mol.**

56.
A chemist weighs 10 g of water, 10 g of ammonia and 10 g of hydrogen chloride.
Calculate the total number of moles contained in the mixture?

**Ans: 1.4 moles**

57.
Give the mass of a silver atom?

**Ans: 1.794 x 10 ^{-22}
**

58.
Determine the number of molecules contained in a drop of water weighing 0.04 g?

**Ans: 1.34 x 10 ^{21}
molecules**

59.
Express 0.000000367 in scientific notation and calculate the significant
figures?

**Ans: 3.67 x 10 ^{-7}
; Number of significant figures is 3**

60.
What is the mass of HCl required to neutralise completely 5g of NaOH?

**Ans: 4.545 g**

61.
Which contains more molecules: 1 g of sulphur dioxide or 1 g of sulphur
trioxide?

**Ans: 1 g of SO _{2}**

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