at stp x ml n2 gas react completely with x ml o2 gas and form a gas a. what will be the molecular formula of a if volume is unchanged after reaction?

Answer 1

I think it's easier if we assign some number for x so let's use something easy like 200 ml
.........N2 + O2 ---> NyOz
I.......200.....200....0
C...-200....-200.....+ 400
E.....0...........0..........400
The problem tells us that we start off with a total volume of 400 and that the reaction is complete and that the initial volume = final volume.
Therefore, N2 + O2 ==> N2O2 but since the final volume must be twice N2 and twice O2 then N2 +O2 --> 2NO
NO is the molecular formula.

Answer 2

OR
....................N2 + O2 ==> NyOz
I....................x........x............0
C..................-x......-x............2x
E...........................................2x
so
.........................N2 + O2 ==> 2NO
Therefore, y and z must be 1 to make the equation balance.