Which one of the following has maximum number of atoms?(a) 18 g of H 2 O(b) 18 g of O 2(c) 18 g of CO 2(d) 18 g of CH

To answer this question, we need to calculate the number of moles in each substance, because 1 mole of any substance contains the same number of atoms (Avogadro's number, 6.022 x 10^23 atoms/mole).

The number of moles is calculated by dividing the mass of the substance by its molar mass.

(a) For H2O, the molar mass is 18 g/mole. So, 18 g of H2O is 1 mole, which contains 6.022 x 10^23 molecules. Since each molecule of H2O contains 3 atoms (2 hydrogen atoms and 1 oxygen atom), the total number of atoms is 3 x 6.022 x 10^23 = 1.8066 x 10^24 atoms.

(b) For O2, the molar mass is 32 g/mole. So, 18 g of O2 is 0.5625 mole, which contains 0.5625 x 6.022 x 10^23 = 3.387 x 10^23 molecules. Since each molecule of O2 contains 2 atoms, the total number of atoms is 2 x 3.387 x 10^23 = 6.774 x 10^23 atoms.

(c) For CO2, the molar mass is 44 g/mole. So, 18 g of CO2 is 0.4091 mole, which contains 0.4091 x 6.022 x 10^23 = 2.463 x 10^23 molecules. Since each molecule of CO2 contains 3 atoms, the total number of atoms is 3 x 2.463 x 10^23 = 7.389 x 10^23 atoms.

(d) For CH4, the molar mass is 16 g/mole. So, 18 g of CH4 is 1.125 moles, which contains 1.125 x 6.022 x 10^23 = 6.774 x 10^23 molecules. Since each molecule of CH4 contains 5 atoms, the total number of atoms is 5 x 6.774 x 10^23 = 3.387 x 10^24 atoms.

So, 18 g of CH4 has the maximum number of atoms.