Question

a) An element 'X' has valency 3. Write its chemical formulae with sulphate ions.
b) An element 'E' shows two valencies 2 & 4 .write the chemical formulae of the two oxides of 'E'.
c) An element Y has valency one.Write its formula with carbonate ion.

Answer 1

A) valancy of element X is 3 and  valency of sulphate ion is 2 as sulphate ion is SO4^2-
the chemical formula would be X2(SO4)2
B) valancy of oxide is 2 (O^2-)
if the valency of element E is 2
the chemical formula would be EO
if the valency of element E is 4
the chemical formula would be EO2
C) valency of element Y is 1
valency of carbonate ion (CO3^2-) is 2
the chemical formula would be Y2CO3

Answer 2

A) X2(SO4)3

B) 1] EO {E->2}
     2] E2O4 or EO2 {E->4}

C) Y2(CO3)