1

### 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

### 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

### 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

### 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.