Carbon reacts with hot concentrated nitric acid then
conc. nitric acid oxidises non-metal carbon to their corresponding oxy acid and itself gets reduced to Brown coloured gas nitrogen dioxide.
$\mathrm{C}+\underset{\mathrm{conc}.}{4{\mathrm{HNO}}_3}\to {\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}+4{\mathrm{NO}}_2$