Question

salt 'A'on heating gives a reddish brown coloured gas 'B'a colourless, odourless gas
' C' and a residue 'D',yellow when hot and white when cold​

Answer 1

This white crystalline solid is Lead Nitrate[Pb(NO3) 2].On heating, it decomposes and leaves behind a residue lead oxide(PbO) i. e yellow in colour which soon changes its colour and brown fumes of nitrogen dioxide (NO2) gas along with oxygen.

The reaction is:

2Pb(NO3) 2-->2PbO + 4NO2+O2

Hope it helps you.

Answer 2

Given:

(i) salt 'A'on heating gives a reddish brown coloured gas 'B'

(ii) A colourless, odourless gas, 'C'

(iii) A residue 'D', which is yellow when hot and white when cold.

To find:

(i) A, B, C and D.

Solution:

We know that if lead nitrate, Pb(NO₃)₂, is heated, it gives off lead (II) oxide, PbO, NO₂ gas and O₂ gas.

The reaction is as follows:

2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

We know that the residue formed after heating, PbO, shows a colour which is yellow when hot and white when cold.

Thus D is PbO.

The gases released - Nitrogen dioxide, NO₂ is reddish brown in colour whereas oxygen, O₂ is colourless. Thus,

B is NO₂ and

C is O₂.

And the reagent, the salt is Pb(NO₃)₂.

So, A is Pb(NO₃)₂.

B is NO₂  

C is O₂

D is PbO.