For each of the 3 ionic compounds, select the main group element "X" belongs to ...

a) X3PO4

b) CaX2

c) X2 (SO4) 3

a) X belongs to Group 1A

b) X belongs to Group 7A

c) x belongs to Group 3A

Explanation:

It is important to know the oxidation number of the elements in order to understand how the answers were obtained.

The oxidation number is obatined from their valency (or put it simply, group number).

Also, the oxidation number of a molecule is Zero.

In the first option,

O has an ox. number of - 2, P has an ox. number of + 5, and the molecule has an ox number of 0.

In the form of an equation we have,

3 (x) + 5 + 4 (-2) = 0

3x + 5 - 8 = 0

3x - 3 = 0

x = 3/3

x = 1 (Group 1).

In the second option,

Ca has an ox. number of + 2, and the molecule has an ox. number of 0.

In the form of an equation we have,

2 + 2 (x) = 0

2x = - 2

x = - 2/2

x = - 1

This means it needs one mre electron to complete its octet. a characteristic of the group 7 elements.

In the third option,

S has an ox. number of + 6, O has an ox. number of + 2 and the molecule has an ox. number of 0.

In the form of an equation we have,

2 (x) + 3[6 + 4 (-2) ] = 0

2x + 3 (-2) = 0

2x = 6

x = 6/2 = 3 (Group 3)