1

### JEE Main 2017 (Online) 9th April Morning Slot

Adsorption of a gas on a surface follows Freundlich adsorption isotherm. Plot of log ${x \over m}$ versus log p gives a straight line with slope equal to 0.5, then:

( ${x \over m}$ is the mass of the gas adsorbed per gram of adsorbent)
A
B
Adsorption is proportional to the pressure.
C
Adsorption is proportional to the square root of pressure.
D
Adsorption is proportional to the square of pressure.

## Explanation

According to Freundlich adsorption isotherm, in the median range of pressure

${x \over m} \propto {P^{{1 \over n}}}$

$\Rightarrow$  ${x \over m}$ = kP$^{{1 \over n}}$

taking log both sides, we get,

log${x \over m}$ = logk + ${1 \over n}$ logP

Here in graph between log${x \over m}$ and logP, slope is ${1 \over n}$ and intercepts = log k.

Given that,

slope = 0.5

$\therefore\,\,\,$ ${1 \over n}$ = 0.5

$\Rightarrow$   n = 2

$\therefore\,\,\,$ ${x \over m}$ = kP$^{{1 \over 2}}$ = k$\sqrt P$

$\therefore$  Adsorption is proportional to the square root of pressure.
2

### JEE Main 2018 (Offline)

Which type of ‘defect’ has the presence of cations in the interstitial sites?
A
Metal deficiency defect
B
Schottky defect
C
Vacancy defect
D
Frenkel defect

## Explanation

In Frenkel defect in a molecule an atom or ion (normally the cation) leave their original site and places itself in the interstitial site (area between all other cations and anions). Which is shown below

3

### JEE Main 2018 (Online) 15th April Morning Slot

Which of the following statements about colloids is False ?
A
Freezing point of colloidal solution is lower than true solution at same concentration of a solute.
B
Colloidal particles can pass through ordinary filter paper.
C
When silver nitrate solution is added to potassium iodide solution, a negatively charged colloidal solution is formed.
D
When excess of electolyte is added to colloidal solution, colloidal particle will be precipitated.

## Explanation

Freezing point of colloidal solution is same as true solution at same concentration of a solute.
4

### JEE Main 2018 (Online) 15th April Morning Slot

Which of the following arrangements shows the schematic alignment of magnetic moments of antiferromagnetic substance ?
A
B
C
D

## Explanation

In antiferro magnetic substance, magnetic dipoles are in opposite direction and cancel out eachother's magnetic moment.