What is the number of molecules in 19.5 L of nitrogen gas at STP

5.24×10²³ molecules of N₂ are in 19.5L of gas

Explanation:

In order to find out the number of molecules, we need to know the mass of N₂ and we must use density of N₂ for that propose

N₂ density = N₂ mass / N₂ volume

N₂ density . N₂ volume = N₂ mass → 1.25 g/L . 19.5 L = 24.4 g

Molar mass N₂ = 28 g/mol → 1 means that 1 mol of N₂ weighs 28 g, so as 1 mol is 28 g and 1 mol contains 6.02×10²³ molecules, 6.02×10²³ molecules are contained in 28 g. Let's make a rule of three, for this:

28 g of N ₂ contain 6.02×10²³ molecules

Then, 24.4 g of N₂ may contain (24.4 . 6.02×10²³ ) / 28 = 5.24×10²³ molecules

the answer would be a