1

### NEET 2017

Which one of the following statements is not correct?
A
The value of equilibrium constant is changed in the presence of a catalyst in the reaction at equilibrium.
B
Enzymes catalyse mainly bio-chemical reactions.
C
Coenzymes increase the catalytic activity of enzyme.
D
Catalyst does not initiate any reaction.

## Explanation

A catalyst accelerates the forward and backward reaction to the same extent thus, the equilibrium constant does not change. Catalyst only speed up the reactions to attain equilibrium faster and does not alter equilibrium constant. Equilibrium constant varies only when temperature condition of reaction gets changed.
2

### NEET 2016 Phase 1

Fog is a colloidal solution of
A
solid in gas
B
gas in gas
C
liquid in gas
D
gas in liquid.

## Explanation

Fog is a colloidal system having dispersed phase as liquid and dispersion medium as gas.
3

### NEET 2016 Phase 2

The coagulation values in millimoles per litre of the electrolytes used for the coagulation of As2S3 are given below :
I.  (NaCl) = 52,
II. (BaCl2) = 0.69,
III. (MgSO4) = 0.22
The correct order of their coagulating power is
A
I > II > III
B
II > I > III
C
III > II > I
D
III > I > II

## Explanation

As,

Coagulating power $\infty$
1
Coagulation value

Lower the coagulation value, higher is the coagulating power so, the correct order is :

III > II > I
4

### NEET 2016 Phase 1

Which one of the following characteristics is associated with adsorption?
A
$\Delta$G and $\Delta$H are negative but $\Delta$S is positive.
B
$\Delta$G and $\Delta$S are negative but $\Delta$H is positive.
C
$\Delta$G is negative but $\Delta$H and $\Delta$S are positive.
D
$\Delta$G, $\Delta$H and $\Delta$S all are negative.

## Explanation

Adsorption is spontaneous process, therefore change in the free energy ( $\Delta$G) for the process is negative.

As we know that

$\Delta$G = $\Delta$H – T$\Delta$S

S is negative because adhering of gas molecules to the surface lowers the randomness.

$\therefore$ $\Delta$G can be –ve only when $\Delta$H is –ve.