ANSWER
The formula of strontium oxide is SrO
EXPLANATION
Strontium oxide is formed when strontium reacts with oxygen
Below is the reaction between strontium and oxygen
[tex]\text{ Sr}_{(s)}\text{ }+\text{ }\frac{1}{2}O_{2(g)}\text{ }\rightarrow\text{ SrO}[/tex]Hence, the formula of strontium oxide is SrO