Question

___Ca2+ + ___O2 ---> Cr2O3

Answer 1

Balancing chemical equations is my priority!! :-)

`Ca_(2)` +
`O_(2)` =
`Ca_(2) O_(3)`

On both sides Calcium (Ca) is balanced ( 2 and 2 )

Then Oxygen (O) is 2 on the reactant side and 3 on the product side.

Divide the subscripts (product subscript/reactant subscript) to give 1.5 (3/2)

Because you can't put 1.5 in an equation you multiply everything by 2.

Then it comes
`2Ca_(2)` +
`3O_(2)` =
`2Ca_(2) O_(3)`

Have a wonderful day! :-)