Question

In which compound is the percent by mass of oxygen greatest?

A. BeO
B. MgO
C. CaO
D. SrO

Answer 1

The answer is A
Hide the Oxygen for a minute
Mass of elements:
Be:9.012
Mg:24.305
Ca:40.078
Sr:87.62
Out of all these choices, Be is the lightest

Answer 2

Answer: BeO

Explanation:

percent by mass of oxygen
`=\frac{\text {mass of oxygen}}{\text {Total mass of substance}}* 100\%`

percent by mass of oxygen in BeO
`=(16g)/(25.01g/mol)* 100=63.97\%`

percent by mass of oxygen in MgO
`=(16g)/(40.30g/mol)* 100=39.70\%`

percent by mass of oxygen in CaO
`=(16g)/(56.08g/mol)* 100=28.53\%`

percent by mass of oxygen in SrO
`=(16g)/(103.62g/mol)* 100=15.44\%`