Which of the following statements about nitric acid are correct?

ACopper reacts with concentrated $HNO X_{3}$ mainly to give $NO$ .
BConcentrated $HNO X_{3}$ oxidises iodine to iodic acid, $HIO X_{3}$ .
CGold dissolves in concentrated $HNO X_{3}$ alone.
DThe yellow-brown colour of old concentrated $HNO X_{3}$ is due to dissolved $NO X_{2}$ formed by its decomposition in light.

Answer: B, D

I X_{2} + 10 HNO X_{3} 2 HIO X_{3} + 10 NO X_{2} + 4 H X_{2} O

. Gold needs aqua regia (conc.

HNO X_{3}

: conc.

HCl

= 1:3).

4 HNO X_{3} 4 NO X_{2} + O X_{2} + 2 H X_{2} O

on exposure to light gives the yellow-brown colour. Copper gives mainly

NO X_{2}

with the concentrated acid, and

NO

with the dilute acid. Correct: A, C.