1

### JEE Main 2018 (Online) 16th April Morning Slot

A group 13 element 'X' reacts with chlorine gas to produce a compound XCl3. XCl3 is electron deficient and easily reacts with NH3 to form Cl3X $\leftarrow$ NH3 adduct ; however, XCl3 does not dimerize X is :
A
B
B
Al
C
Ga
D
In

## Explanation

Here BCl3 is electron deficient compound as B has 6 electrons. That is why it accept electron pair from NH3 to form an adduct.

BCl3 does not form dimer like Al, Ga or In, because its electron deficiency is complemented by the formation of co-ordinate bond between lone pair of electron of chlorine and empty unhybridized P-orbital of boron forming P$\pi$ $-$ P$\pi$ bonding.
2

### JEE Main 2019 (Online) 9th January Morning Slot

Correct statements among a to d regarding silicones are :

(a)   They are polymers with hydrophobic character.
(b)   They are biocompatible.
(c)   In general, they have high thermal stability and low dielectric strength.
(d)   Usually, they are resistant to oxidation and used as greases.
A
(a), (b), (c) and (d)
B
(a), (b) and (c) only
C
(a) and (b) only
D
(a), (b) and (d) only

## Explanation

(a) and (b) are properties of silicone.
(d) is the uses of silicone.
3

### JEE Main 2019 (Online) 9th January Morning Slot

The one that is extensively used as a piezoelectric material is :
A
tridymite
B
amorphous silica
C
quartz
D
mica

## Explanation

Those materials which produce electricity under mechanical stress are called piezoelectric material.

Quartz is an example of piezoelectric material.
4

### JEE Main 2019 (Online) 9th January Evening Slot

Good reducing nature of H3PO2 is attributed to the presence of :
A
Two P $-$ OH bonds
B
One P $-$ H bond
C
Two P $-$ H bonds
D
One P $-$ OH bond

## Explanation

H3PO2 is good reducing agent due to presence of two P $-$ H bonds.