Question

molecules having one kind of atoms only and next question is molecules having two different kind of atoms and next question is three different kind of atoms

Answer 1

oxygen
water
KOH
hope it helps u

Answer 2

1.Molecules  having one kind of atoms are Nitrogen[N2], O2, H2 etc.
2. Molecules having different kinds of atoms are H2O, CO2,NH3,SO2 etc.
3.. Molecules having three different kinds of atoms: KMnO4, K2CrO7 etc..