1 mole of all gases at STP conditions occupy a volume of 22.4 L.
So, 1 mole of all gases at STP conditions occupy a volume of 22.4 L is a true statement.
Assertion (A): One gram molecule of any gas occupies 22.4 L volume at STP.
Reason (R): Under similar conditions of temperature and pressure equal masses of all gases occupy equal volumes.