We’re being asked to identify which of the given processes is endothermic. 

Recall that:

• Exothermic reactions

▪ lose energy, releases heat, the temperature of the surroundings increases
▪ involves bond formation (for phase change: gas → liquid → solid)
▪ ΔH is negative

• Endothermic reactions

▪ gain energy, absorbs heat, the temperature of the surroundings decreases
▪ involves breaking bonds (for phase change: solid → liquid → gas)
▪ ΔH is positive