Question

which metal forms peroxides in preference to its oxides
lithium
sodium
or potassium

Answer 1

lithium form peroxide in preference to it's oxides because it is a alkali metal and it is more reactive than sodium and potassium and forms lithium peroxide i.e. Li2O

Answer 2

Correct answer is the second option -  Sodium.

More details on the formation of oxides, peroxides and superoxides are as follows:

• Lithium forms oxides more preferably. The tiny Lithium ion has stronger positive field and restricts it from forming higher oxides.
• Sodium forms peroxides in preference to its other oxides. When compared to Lithium, Sodium ion has weak positive field. Thus oxides convert into peroxides.
• Similarly, Potassium readily forms superoxides.

Hope it helps.