Question

Which of the following pairs does not share the same empirical formula?
CH2O and C3H6O3
PbCl2 and PbCl4
NO2 and N2O4
C3H12 and CH4

Answer 1

firstly, do you know what is empirical formula?

Answer 2

no

Answer 3

its the lowest ratio between atoms forming a compound is its empirical formula
for example:
if you have an original compound: C6H12
ratio between them is
6 : 12
now divide both ratios to a same number, that can lead you to the lowest ratio between them
this number would be 6 in this case
6/6 : 12/6
1 : 2
so lowest ratio possible is 1 : 2
thus empirical formula is CH2

**********one more example: C6H12O6
now you have 3 different atoms in one compound
lets do ratio again
6 : 12 :6
now again find a number that you can divide all these ratios by, and get the lowest ratio between them
so its again 6
6/6 : 12/6 : 6/6
thus
1 : 2 : 1
so empirical formula
CH2O

i hope you understand now?