Alkynes are more reactive than alkynes towards addition reaction but the opposite is true in case of catalytic hydrogenation. Why?

The alkynes are less reactive than alkynes towards halogens toon. Why?

Arrange the following in the order of their increasing order of expected enol content. H3C-CO-CH2-CHO, H3C-CO-CH3, H3C-CHO and H3C-CO-CH2-CO-CH3 .

As the substituents at the enolic double bond in the enol increases, the enolic content increases.