The half-life of cobalt-69 is 6 years. How much of a 5-gram sample is left after 12 years

that was wrong my bad. just delete my answer

Explanation:

The number of moles represented by 21.7 L is 0.96875 moles

Explanation:

The volume occupied by one mole of a gas which consists of (approximately) 6.022 × 10²³ elementary at STP is 22.4 L. The volume is known as the molar volume of gas

Therefore, the number of moles, 'n', present in 21.7 L of gas at STP is given as follows;

The number of moles represented by 22.4 L = 1 mole

∴ The number of moles represented by 21.7 L = 1 mole/22.4 L × 21.7 L = 0.96875 moles

The number of moles represented by 21.7 L = 0.96875 moles.