Lithium aluminium hydride ($LiAlH_4$) is a strong reducing agent that affects nitrogen-containing functional groups differently:

1. Isocyanides ($R-NC$): Reduction yields secondary amines ($R-NH-CH_3$). Specifically, methyl isocyanide ($CH_3NC$) is reduced to dimethylamine ($CH_3-NH-CH_3$), which is a secondary amine .
2. Amides ($R-CONH_2$): Reduction yields primary amines ($R-CH_2-NH_2$). Acetamide ($CH_3CONH_2$) gives ethylamine .
3. Cyanides/Nitriles ($R-CN$): Reduction yields primary amines ($R-CH_2-NH_2$). Methyl cyanide ($CH_3CN$) gives ethylamine .
4. Nitroalkanes ($R-NO_2$): Reduction yields primary amines ($R-NH_2$). Nitroethane gives ethylamine .

Therefore, only Methyl isocyanide yields a secondary amine.