Number of moles of the gas = $0.1\text{ mol}$. Number of molecules in $0.1\text{ mol}$ of the gas = $0.1 \times N_A = 0.1 \times 6.02 \times 10^{23} = 6.02 \times 10^{22}\text{ molecules}$. Since it is a triatomic gas, each molecule contains $3\text{ atoms}$. Therefore, the total number of atoms = $3 \times 6.02 \times 10^{22} = 18.06 \times 10^{22} = 1.806 \times 10^{23}\text{ atoms}$.