K + O₂ \(\longrightarrow \) KO₂, potassium superoxide will be formed.

This is due to abnormal increase in the atomic size of potassium.

s-block contains only two groups; group 1 (alkali metals) and group 2 (alkaline earth metals)

Since, among alkali metals, lithium has the most negative electrode potential (E^o = -3.04 V) so, it is the strongest reducing agent in the aqueous solution.

Valence electrons of alkali metals like Na and K easily absorb energy from the flame and are excited to higher energy levels. When these electrons return to the ground state, the energy is emitted in the form of light.
Magnesium atom has small size so electrons are strongly bound to the nucleus Thus they need large amount of energy for excitation of electrons to higher energy levels which is not possible in bunsen flame.

MgCl₂ \(\xrightarrow []{electrolysis} \)Mg2⁺+2 Cl^-
At cathode
Mg²⁺(aq)+2e^-\(\longrightarrow \)Mg(s)
At anode
2Cl^-(aq)-2e^- \(\longrightarrow \)Cl₂(g)

Sodium ions:
(i) Na⁺ ions participate in the transmission of nerve signals, in regulating the flow of water across cell membranes.
(ii) In the transport of sugars and amino acids into cell.
Potassium ions:
(i) They activate many enzymes.
(ii) Participate in the oxidation of glucose to produce ATP.
Magnesium ions:
(i) All enzymes that utilise ATP in phosphate transfer require magnesium as a cofactor.
(ii) Mg is the main pigment for the absorption of light in plants.
Calcium:
(i) Ca²⁺ ions are present in bones.
(ii) plays important roles in neuromuscular function

Sodium peroxide It is obtained by heating sodium metal (Which is obtained ny the electrolysis of molten NaCl), in excess of air. The initially formed sodium oxide reacts with more O2 to form Na₂O₂.   
4Na + O₂ \(\xrightarrow{\Delta}\)  2 Na₂O₂ 2Na₂O;
2Na₂O + O₂ + O₂\(\xrightarrow{\Delta}\)  2 Na₂O₂ ;

sodium hydroxide It is manufactured by eectrolysis of an aqueous solution of NaCl(brine ) in Castner - Kelner Cell using mercury cathode and carbon anode. Sodium metal which is discharged at the cathode combines with mercury to form sodium amalgam.Cl₂ gas with mercury to form sodium amalgham .Cl₂ gas is evolved at the anode.
At cathode  Na⁺ +e^- \(\xrightarrow [ ] {Hg}\) na-amalgram
At anode 2 Cl^- \(\rightarrow\)Cl₂ +2e^-
The sodium amalgam  thus obtained is treated with water to form sodium hydroxide and hydrogen gas.
2Na-amalgam +2H₂O\(\rightarrow\) 2 NaOH + 2Hg + H₂