1

### JEE Main 2016 (Online) 9th April Morning Slot

A particular adsorption process has the following characteristics : (i) It arises due to van der Waals forces and (ii) it is reversible. Identify the correct statement that describes the above adsorption process :
A
Enthalpy of adsorption is greater than 100 kJ mol−1.
B
Energy of activation is low.
C
D
Adsorption increases with increase in temperature.
2

### JEE Main 2016 (Online) 10th April Morning Slot

Gold numbers of some colloids are : Gelatin : 0.005 - 0.01, Gum Arabic : 0.15 - 0.25; Oleate : 0.04 - 1.0; Starch : 15 - 25. Which among these is a better protective colloid ?
A
Gelatin
B
Gum Arabic
C
Oleate
D
Starch
3

### JEE Main 2017 (Offline)

A metal crystallises in a face centred cubic structure. If the edge length of its unit cell is ‘a’, the closest approach between two atoms in metallic crystal will be:
A
$2\sqrt 2 a$
B
$\sqrt 2 a$
C
${a \over {\sqrt 2 }}$
D
2a

## Explanation

For a fcc unit cell

$r = {{\sqrt 2 a} \over 4}$

$\therefore$ Closest distance (2r) = ${{\sqrt 2 a} \over 4} = {a \over {\sqrt 2 }}$
4

### JEE Main 2017 (Offline)

The Tyndall effect is observed only when following conditions are satisfied:
(a) The diameter of the dispersed particles is much smaller than the wavelength of the light used.
(b) The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
(c) The refractive indices of the dispersed phase and dispersion medium are almost similar in magnitude.
(d) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.
A
(b) and (d)
B
(a) and (c)
C
(b) and (c)
D
(a) and (d)

## Explanation

Tyndall effect is observed only when

(i) The diameter of the dispersed particle is not much smaller than the wavelength of the light used.

(ii) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.

So, (b) and (d) are correct.