b
\((b)\) Most stable alkene less heat of hydrogenation.
\(a \to 4\, \alpha \,H\)                   Heat of hydrogenation \(\to d > a > c > b\)
\(b \to 10\,\alpha \,H\)
\(c \to 6\,\alpha \,H\)
\(d \to 3 \,\alpha \,H\)