What volume of oxygen is produced at STP when 3.56 x 10^24 molecules of water is
decomposed into hydrogen gas and oxygen gas.

64.96 litre of oxygen is produced at STP when 3.56 x 10^24 molecules of water is  decomposed into hydrogen gas and oxygen gas.

Explanation:

The balance equation for the decomposition of water in to hydrogen gas and oxygen gas is:

2H20  2H2+ 02

the oxygen formed from the decomposition reaction is 0.5 moles

So, number of molecules of oxygen are

0.5*3.56*10^24

= 1.78 *10^23  moles of oxygen gas produced.

We know that 1 mole contains

6.023*10^23 particles

So total amount produced is:

1.78*10^24/6.02*10^23

2.9 moles

we know that at STP, the temperature is 273K, Pressure is 1 atm, volume is 22.4 litres

So the volume of oxygen produced will be given by:

22.4*2.9

=64.96 Litres