At STP, 1 mole of any gas occupies 22.4 L. The molar mass of krypton (Kr) is 83.798 g/mol.

To calculate the volume of 0.405 g of krypton gas at STP, we can use the following formula:

Volume = (Mass of gas / Molar mass) x 22.4 L/mol

Substituting the given values into the formula, we get:

Volume = (0.405 g / 83.798 g/mol) x 22.4 L/mol

Volume = 0.0107 L

Therefore, 0.405 g of krypton gas will occupy 0.0107 L at STP.