elements are made of one type of atoms. Elements have characteristic symbols for their identification.
1) Bi(NO₃)₃ - this is made of 3 elements - Bismuth , Nitrogen and oxygen
2) KOH - made of 3 elements - potassium (K), oxygen and hydrogen
3) NaClO₃ - made of 3 elements - sodium (Na), chlorine and Oxygen
4) Al₂S₃ - made of 2 elements - Aluminium and sulphur
we are asked for the formula with 2 elements , correct answer is 4)
