Which of the following is a correct formula unit of an ionic compound? al2f3 ca2o ca(oh)2 kcl2

Answer : The correct formula unit of an ionic compound is Ca(OH)2

Explanation :

An ionic compound is formed when a metal atom donates one or more electrons to a non metal atom.

During this process, metal gains a positive charge and a nonmetal gets a negative charge.

In an ionic compound, these charges on the ions are balanced so that the overall compound is neutral.

Let us check which of the given compounds have a neutral charge.

1) Al2F3 : Charge on Al is +3 and that on F is -1.

The total charge on 2 Al is 2x3 = +6.

The total charge on 3 F atoms is 3x(-1) = -3

The overall charge on the compound is +6-3 = +3.

That means the given formula unit is not correct.

2) Ca2O : Charge on Ca is +2 and that on O is -2

Total charge on Ca is 2x2 = +4

The overall charge is +4-2 = +2

Therefore the given formula unit is not correct.

3) Ca(OH)2 : The charge on Ca ion is +2 and that on OH is -1.

The total charge on 2 OH ions is 2x(-1) = -2

The overall charge is +2-2 = 0

This gives a neutral compound.

Therefore the given formula unit is correct.

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