CBSE Class 10 Science 2019 · Paper 31/2/1 · Question 6

(a) It is a thermal decomposition reaction (a decomposition reaction brought about by heat). The brown gas X is nitrogen dioxide, ${\text{NO}}_2$. (b) $2{\text{Cu(NO}}_3{\text{)}}_2(s)\stackrel{\text{heat}}{\to }2\text{CuO}(s)+4{\text{NO}}_2(g)+{\text{O}}_2(g)$ (c) ${\text{NO}}_2$ is a non-metal oxide and dissolves in water to give an acidic solution, so its pH is less than $7$: it lies in the acidic range, from $0$ up to but not including $7$.