1
MCQ (Single Correct Answer)

AIPMT 2008

Volume occupied by one molecule of water (density = 1 g cm$$-$$3) is
A
3.0 $$ \times $$ 10$$-$$23 cm3
B
5.5 $$ \times $$ 10$$-$$23 cm3
C
9.0 $$ \times $$ 10$$-$$23 cm3
D
6.023 $$ \times $$ 10$$-$$23 cm3

Explanation

1 mole of water contains 6.023 × 1023 molecules of water

6.023 × 1023 molecules of water weigh = 18 g

So, 1 molecule of water weighs = $${{18} \over {6.023 \times {{10}^{23}}}}$$

Now, volume of 1 molecule of water

=
Mass of 1 molecule of water
Density of water
.

= $${{18} \over {6.023 \times {{10}^{23}}}} \times {1 \over {1\,g\,c{m^{ - 3}}}}$$

= 3 $$ \times $$ 10-23 cm3
2
MCQ (Single Correct Answer)

AIPMT 2008

If a gas expands at constant temperature, it indicates that
A
kinetic energy of molecules remains the same
B
number of the molecules of gas increases
C
kinetic energy of molecules decreases
D
pressure of the gas increases.

Explanation

Kinetic energy of a gas is expressed as

K.E = $${3 \over 2}nRT$$

Thus, on expansion of fixed amount of gas at constant temperature the kinetic energy remains constant.
3
MCQ (Single Correct Answer)

AIPMT 2002

Van der Waal's real gas, acts as an ideal gas, at which conditions?
A
High temperature, low pressure
B
Low temperature, high pressure
C
High temperature, high pressure
D
Low temperature, low pressure

Explanation

At higher temperature and low pressure real gas acts as an ideal gas.
4
MCQ (Single Correct Answer)

AIPMT 2001

The beans are cooked earlier in pressure cooker because
A
boiling point increases with increasing pressure
B
boiling point decreases with increasing pressure
C
extra pressure of pressure cooker softens the beans
D
internal energy is not lost while coocking in pressure cooker.

Explanation

When water pressure increases in the pressure cooker, water boils at lower temperature and the beans in pressure cooker are cooked earlier.

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