Question

An element reacts with oxygen to form an oxide which turns a solution of red litmus toblue

Answer 1

the element is a metal as we know that metal react with oxygen to form oxide. metal as only they only to form basic oxide.

Base turn the red litmus into blue and metal oxides are basic in nature.
for example 2Mg + O2 --- 2MgO

MgO is a metal oxide so it is basic in nature. so it turn red litmus into blue.