Which reaction is single replacement?

(1) 2H2O2 - - > 2H2O + O2

(2) 2H2 + O2 - - > 2H2O

(3) H2SO4 + Mg - - > H2 + MgSO4

(4) HCl + KOH - - > KCl + H2O

In a single replacement reaction (or simple displacement) an element reacts with a compound and takes the place of another element in that compound. The reaction that shows a sigle replacement is the third one. Where H2SO4 and Mg turn into H2 + MgSO4. In this case Mg replaces H2

Among the given choices, the third option is the only one which illustrates single replacement. (3) H2SO4 + Mg - - > H2 + MgSO4 A single replacement is also termed as single-displacement reaction, a reaction by which an element in a compound, displaces another element. It can be illustrated this way: X + Y-Z → X-Z + Y