Find the number of water molecules in 1 mL of water vapours at STP?

Step-by-step solution

Calculating water molecules in 1 mL vapor at STP Standard Temperature and Pressure conditions define molar gas volume as 22.4 L/mol. For water vapor occupying 1 mL = 1 10⁻³ L , the number of moles is n = 1 10⁻³ 22.4 = 1 22400 mol . Using Avogadro's number N_A = 6.022 10²³ molecules/mol , the molecular count becomes n N_A = 1 22400 6.022 10²³ . This simplifies to approximately 2.69 10¹⁹ molecules, corresponding to option D.