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1

### NEET 2021

Choose the correct option for the total pressure (in atm.) in a mixture of 4g O2 and 2g H2 confined in a total volume of one litre at 0$$^\circ$$C is :

[Given R = 0.082 L atm mol$$-$$1K$$-$$1, T = 273 K]
A
26.02
B
2.518
C
2.602
D
25.18

## Explanation

$${n_{{O_2}}} = {4 \over {32}} = {1 \over 8}$$

$${n_{{H_2}}} = {2 \over 2} = 1$$

$${n_t} = {1 \over 8} + 1 = {9 \over 8}$$

$${P_t}V = {n_t}RT$$

$${P_t} = {{{9 \over 8} \times 0.082 \times 273} \over 1} = 25.18$$ atm
2

### NEET 2021

Choose the correct option for graphical representation of Boyle's law, which shows a graph of pressure vs. volume of a gas at different temperatures :
A
B
C
D

## Explanation

According to Boyle's law, at constant temperature, pressure of a gas of fixed amount varies inversely with volume.

p $$\propto$$ $${1 \over V}$$ $$\Rightarrow$$ p = $${k \over V}$$ $$\Rightarrow$$ pV = k

where k is proportionality constant and equal to nRT.

As temperature increases, gas expands i.e. volume of gas increases.

So, the product pV increases and the p vs V curve of Boyle’s law shifts upwards.
3

### NEET 2020 Phase 1

A mixture of N2 and Ar gases in a cylinder contains 7g of N2 and 8g of Ar. If the total pressure of the mixture of the gases in the cylinder is 27 bar, the partial pressure of N2 is :
[Use atomic masses (in g mol$$-$$1) : N = 14, Ar = 40]
A
12 bar
B
15 bar
C
18 bar
D
9 bar

## Explanation

$$^n{N_2} = {7 \over {28}} = 0.25$$
$$^n{A_r} = {8 \over {40}} = 0.2$$
Now, applying Dalton's law of partial pressure,
$$^P{N_2} = {{^n{N_2}} \over {^n{N_2}{ + ^n}{A_r}}} \times {P_{Total}}$$
$$= {{0.25} \over {0.45}} \times 27$$ bar
= 15 bar
4

### NEET 2019

A gas at 350 K and 15 bar has molar volume 20 percent smaller than that for an ideal gas under the same conditions. The correct option about the gas and its compressibility factor (Z) is -
A
Z < 1 and attractive forces are dominant
B
Z < 1 and repulsive forces are dominant
C
Z > 1 and attractive forces are dominant
D
Z > 1 and repulsive forces are dominant

## Explanation

Compressibility factor (Z ) = $${{{V_{real}}} \over {{V_{ideal}}}}$$

Here, Vreal < Videal. Therefore, Z < 1.

In gaseous molecules attractive forces are dominant.

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NEET

Class 12