When u use dilute nitric acid, i think there might be possible
multiple substituitions resulting in white ppt. So i dunnoe whether
d is correct orwrong.
And qn 20, why not D?
Updated : Q28 is C, not D (since nitrophenols are yellow
coloured).
Check that your drawing of your skeletal structure for P has the
correct no. of C atoms. Then notice that the 2 terminal methyl
groups are identical. Hence only 5 possible isomers.