An aliphatic nitro compound turns red with the addition of a concentrated $\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\mathrm{ }$solution, followed by the addition of an excess of an $\mathrm{N}\mathrm{a}\mathrm{N}{\mathrm{O}}_2\mathrm{ }$solution and then dilute ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4.$ The colour disappears with the addition of the excess of an acid but reappears if the solution is made alkaline. The aliphatic nitro compound is