Determine the number of electrons for a neutral Magnesium atom.

Magnesium (Mg) has an atomic number (Z) of 12, so a neutral atom has 12 electrons.

The s, p configuration for a neutral Magnesium atom is $\boxed{\text{1s}^2 \text{2s}^2 \text{2p}^6 \text{3s}^2}$.

10 (b)

A $\text{Mg}^{2+}$ ion is formed when a neutral Magnesium atom loses 2 electrons. Electrons are lost from the outermost shell first.

The outermost sub-shell in the neutral Magnesium atom (configuration $1s^2 2s^2 2p^6 3s^2$) is the $3s$ sub-shell.
When Magnesium becomes an ion $\text{Mg}^{2+}$, the $\boxed{\text{3s}}$ sub-shell is emptied.

10 (c)

Neutral Mg: $1s^2 2s^2 2p^6 3s^2$
Removing 2 electrons from the $3s$ sub-shell results in:

The resulting configuration of the $\text{Mg}^{2+}$ ion is $\boxed{\text{1s}^2 \text{2s}^2 \text{2p}^6}$.

11 (a)

Calcium (Ca) is in Group 2, so it forms a $\text{Ca}^{2+}$ ion, meaning its valency is +2.

Since the compound $\text{Ca(ClO)}_2$ is neutral, the total negative charge must balance the +2 charge from Calcium. There are two $\text{ClO}$ radicals, so each $\text{ClO}$ radical must have a valency of -1.
The valency of the Hypochlorite radical ($\text{ClO}$) is $\boxed{\text{-1}}$.

11 (b) (i)

Chlorine (Cl) has an atomic number (Z) of 17, so a neutral atom has 17 electrons.

A $\text{Cl}^{-}$ ion is formed when a neutral Chlorine atom gains 1 electron. So, it has $17 + 1 = 18$ electrons.

The gained electron will fill the $3p$ sub-shell.

The s, p configuration for the $\text{Cl}^{-}$ ion is $\boxed{\text{1s}^2 \text{2s}^2 \text{2p}^6 \text{3s}^2 \text{3p}^6}$.

11 (b) (ii)

Reactants: Calcium ($\text{Ca(s)}$) and Chlorine gas ($\text{Cl}_2\text{(g)}$).
Product: Calcium Chloride ($\text{CaCl}_2\text{(s)}$).

The equation is already balanced with one Ca atom and two Cl atoms on both sides.
The balanced equation with state symbols is: