Which of these compounds have the same empirical formula?

1. The empirical formulae of C₂H₂ and C₆H₆ are CH and CH respectively. They are identical.
2. The empirical formulae of C₂H₆ and C₆H₆ are CH₃ and CH respectively. They are different.
3. The empirical formulae of C₁₂H₈O and C₆H₅OH are C₁₂H₈O and C₆H₆O respectively. They are different.
4. The empirical formulae of NO₂ and N₂O₄ are NO₂ and NO₂ respectively. They are identical.

The answers:
1. C₂H₂ and C₆H₆
4. NO₂ and N₂O₄

4.

1. C2H2 and C6H6
and
4. NO2 and N2O4