The following is/are endothermic reaction (s)

 $H_{2}O\to H_2+\frac{1}{2}{O}_2;\Delta H>0$
It is reverse of combustion of  $H_2\left(g\right)$, hence , endothermic.
 $C_2{H}_6\to C_2{H}_4+H_2;\Delta H>0$
Here, more stable (saturated)
Hydrocarbon is being transformed to less stable (unsaturated) hydrocarbon, hence endothermic.
 $C_{\left(gr\right)}\to C_{\left(d\right)},\Delta H>0$
More stable allotrope is being converted to less stable allotrope