${\mathrm{CH}}_3-\mathrm{NC} \stackrel{\mathrm{HgO}}{\to } \mathrm{X} ;$ The compound ‘X’ is 

${\mathrm{CH}}_3-\mathrm{NCO}$ is methyl isocyanate(MIC). It is a contaminant released from Union carbide factory in Bhopal in the year 1984;