1

### JEE Main 2019 (Online) 11th January Morning Slot

A 10 mg effervescent tablet containing sodium bicarbonate and oxalic acid releases 0.25 ml of CO2 at T = 298.15 K and p = 1 bar. If molar volume of CO2 is 25.0 L under such condition, what is the percentage of sodium bicarbonate in each tablet ?
[Molar mass of NaHCO3 = 84 g mol–1]
A
33.6
B
0.84
C
8.4
D
16.8

## Explanation

2NaHCO3 + (COOH)2 $\to$ (COONa)2 + 2H2O + 2CO2

$\therefore$ 1 mole of CO2 is produced by 1 mole of NaHCO3.

Given, volume of CO2 produced = 0.25 ml

25 L of CO2 contains 1 mol

$\therefore$ 0.25 ml of CO2 contains = ${1 \over {25 \times {{10}^3}}} \times 0.25$ moles

= 10-5 moles

$\therefore$ Moles of NaHCO3 = 10-5 moles

Mass of NaHCO3 = 10-5 $\times$ 84 g

$\therefore$ % of NaHCO3 in a tablet

= ${{84 \times {{10}^{ - 5}}} \over {10 \times {{10}^{ - 3}}}} \times 100$ = 8.4 %
2

### JEE Main 2019 (Online) 11th January Evening Slot

In the following compound,

the favourable site/s for protonation is/are :
A
(b), (c) and (d)
B
(a) and (e)
C
(a) and (d)
D
(a)

## Explanation

At (a) position lone pair of N atom is in resonance with $\pi$ bond so lone pair can't donate easily to H+ ion.

At (b) position N atom is directly connected with double bond so lone pair of N atom don't perticipate in resonance so lone pair can be donated easily to H+ ion.

At (c) position N atom is directly connected with double bond so lone pair of N atom don't perticipate in resonance so lone pair can be donated easily to H+ ion.

At (d) position N atom is directly connected with double bond so lone pair of N atom don't perticipate in resonance so lone pair can be donated easily to H+ ion.

At (e) position lone pair of N atom is in resonance with $\pi$ bond so lone pair can't donate easily to H+ ion.

$\therefore$ (b), (c) and (d) are the favourable sites for protonation.
3

### JEE Main 2019 (Online) 12th January Morning Slot

Among the following four aromatic compounds, which one will have the lowest melting point ?
A
B
C
D

## Explanation

More the intermolecular interaction more will be the melting point. Among the given, naphthalene has least intermolecular interaction and hence it has lowest melting point.

M.P. of Napthalene = 80°C
4

### JEE Main 2019 (Online) 12th January Morning Slot

The increasing order of reactivity of the following compounds towards reaction with alkyl halides directly is

A
A < B < C < D
B
B < A < C < D
C
B < A < D < C
D
A < C < D < B

## Explanation

Lone pair over nitrogen will act as the reacting centre and more free nitrogen atom will be more reactive towards alkyl halide.

For compound (A), lone pair of N atom is in resonance with $\pi$ bond of C = O. So lone pair of N atom gets delocalised.

For compound (B), lone pair of N atom is in resonance with $\pi$ bond of two C = O. So here lone pair of N atom gets more delocalised than compound (A). So reactivity towards alkyl halide is very less for this compound.

For compound (C), lone pair of N atom is in resonance with $\pi$ bond of benzene ring and $\pi$ bond of C $\equiv$ N. So delocalisation of lone pair of N atom is relatively high.

For compound (D), lone pair of N atom is in resonance with $\pi$ bond of benzene ring only. So delocalisation of lone pair of N atom is relatively low.

$\therefore$ Reactivity order is B < A < C < D.