The natural abundance of 2h is 0.015% and that of 18o is 0.20%. how many 2h218o molecules are there in 1.0 moles of water?

Explanation:

Probability of one ²H is 0.00015 = 1.5× 10⁻⁴

Probability of two ²H is 1.5× 10⁻⁴ × 1.5 × 10⁻⁴ = 2.25 × 10⁻⁸

Probability of two ²H plus one ¹⁸O is 2.25 × 10⁻⁸ × 0.0020

= 4.5× 10⁻¹¹

Molecules in 1.0 mol water = 1.0 × 6.022 × 10²³ × 4.5 × 10¹¹

= 2.7 × 10¹³

There are 2.7 × 10¹³ molecules of  ²H₂¹⁸O in 1.0 mol of water.