1

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

For per gram of reactant, the maximum quantity of N2 gas is produced in which of the following thermal decomposition reactions ?
(Given : Atomic wt. - Cr = 52 u, Ba = 137 u)
A
(NH4)2Cr2O7(s) $\to$ N2(g) + 4H2O(g) + Cr2O3(s)
B
2NH4NO3(s) $\to$ 2 N2(g) + 4H2O(g) + O2(g)
C
Ba(N3)2(s) $\to$ Ba(s) + 3N2(g)
D
2NH3(g) $\to$ N2(g) + 3H2(g)

## Explanation

(a)   Molar mass of (NH4)2 Cr2O7 = 252 g/mol.

252g of (NH4)2 Cr2 O7 produce 28g mole of N2

$\therefore\,\,\,$ 1 g of (NH4)2 Cr2 O7 Produce = ${{28} \over {252}} = 0.111$ g N2

(b)    Molar mass of NH4 NO3 = 80 g/mol

2 $\times$ 80 g of NH4 NO3 produce 28 $\times$ 2g of N2

$\therefore\,\,\,$ 1 g of NH4 NO3 produce = ${{28 \times 2} \over {2 \times 80}}$ = 0.35 g N2

(c)    Molar mass of Ba(N3)2 = 221 g/mol

221 g of Ba(N3)2 produce 3 $\times$ 28 g of N2

$\therefore\,\,\,$ 1 g of Ba(N3)2 produce = ${{3 \times 28} \over {221}}$ = 0.38 g of N2

(d)    Molar mass of NH3 = 17 g/mol

17 $\times$ 2 NH3 produce 28 g of N2

$\therefore\,\,\,$ 1 g of NH3 produce = ${{28} \over {17 \times 2}}$ = 0.823 g of N2
2

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

In KO2, the nature of oxygen species and the oxydation state of oxygen atom are, respectively :
A
Oxide and $-$ 2
B
Superoxide and $-$ 1/2
C
Peroxide and $-$ 1/2
D
Superoxide and $-$ 1

## Explanation

KO2 is called potassium superoxide. Here O$_2^ -$ is the superoxide ion.

Oxidation state of K is +1 and let oxidation state of oxygent atom is = x

$\therefore\,\,\,$ 1 + 2(x) = 0

$\Rightarrow$$\,\,\,$ x = $-$ ${1 \over 2}$
3

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

In XeO3F2, the number of bond pair(s), $\pi$-bond(s) and lone pair(s) on Xe atom respectively are :
A
5, 2, 0
B
4, 2, 2
C
5, 3, 0
D
4, 4, 0

## Explanation $\therefore\,\,\,$ Number of Bond pairs = 5

Number of $\pi$ bonds = 3

Number of lone pairs = 0
4

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

Among the oxides of nitrogen : N2O3, N2O4 and N2O5; the molecule(s) having nitrogen-nitrogen bond is / are :
A
Only N2O5
B
N2O3 and N2O5
C
N2O4 and N2O5
D
N2O3 and N2O4

## Explanation $\therefore$   N2O3   and   N2O4   has   N $-$ N   bond.