#### Answer

$C_{13}H_{18}O_2$ is the chemical formula for Ibuprofen

#### Work Step by Step

There are 13 gray spheres, so the formula has 13 carbons: $C_{13}$
There are 18 ivory spheres, so the formula has 18 hydrogens: $H_{18}$
There are 2 red spheres, so the formula has 2 oxygens: $O_2$