How many number of molecules and atoms respectively are present in 2.8 L of a diatomic gas at STP?

Number of molecules of gas at STP = $\frac{6.023\times {10}^{23}\times 2.8}{22.4}$

                                                    $=7.5\times {10}^{22}\text{ molecules }$

Number of atoms in diatomic molecule = $2\times 7.5\times {10}^{22}$

                                                         $=15\times {10}^{22}\text{ atoms }$