Reaction of magnesium ribbon with dilute sulphuric acid to form magnesium sulphate and hydrogen is a combination reaction.
Magnesium is more reactive than hydrogen and it displaces hydrogen from dilute acids. Magnesium reacts with dilute sulphuric acid to form magnesium sulphate and hydrogen gas is evolved. This is a single displacement reaction and also exothermic.
Mg(s)+H2SO4→MgSO4(aq)+H2(g)