(i) Lithium metal is used to make alloys.
(ii) Lithium is also used to make electrochemical cells.
(iii) Lithium carbonate is used in medicines.

The removal of an electron from the alkali metals gives monovalent cations having stable electronic configurations similar to the noble gas. Therefore, it becomes very difficult to remove the second electron from the stable configurations already attained. Hence, the second ionisation enthalpy values of alkali metals are high.

Since ionisation energy values of alkali metals are low, they are very reactive. They readily combine with oxygen, moisture and CO₂ of the atmosphere and form compounds. Hence they do not occur free in nature.

2NH₃ + H₂O + CO₂ ⟶ (NH₄)₂ CO₃
(NH₄)₂ CO₃ + H₂O + CO₂ ⟶ 2NH₄ HCO₃
2NH₄HCO₃ + NaCl ⟶ NH₄Cl + NaHCO₃
2NaH CO₃ ⟶ Na₂ CO₃ + CO₂ + H₂O.

Mg (OH)₂ ; Magnesium hydroxide.

Group 2 elements have positive electron gain enthalpy since they have fully filled s-subshell, they have the least tendency to accept electrons.

(i) Sodium carbonate known as washing soda is used for laundering
(ii) It is an important laboratory reagent used in the qualitative analysis and in volumetric analysis.
(iii) It is also used in water treatment to convert the hard water to soft water
(iv) It is used in the manufacture of glass, paper, paint etc

(i) Lithium metal is used to make useful alloys. For example with lead it is used to make 'white metal' bearings for motor engines, with aluminium to make aircraft parts, and with magnesium to make armour plates. It is used in thermonuclear reactions.
(ii) Lithium is also used to make electrochemical cells.
(iii) Lithium carbonate is used in medicines
(iv) Sodium is used to make Na/Pb alloy.
(v) Liquid sodium metal is used as a coolant in fast breeder nuclear reactors.
(vi) Potassium chloride is used as a fertilizer. Potassium hydroxide is used in the manufacture of soft soap. It is also used as an excellent absorbent of carbon dioxide.
(vii) Caesium is used in devising photoelectric cells.

(i) Due to low ionisation energy K and Cs eject electrons when exposed to light.
(ii) Lithium which has highest ionisation enthalpy among alkali metals cannot be used in photoelectric cells because it does not release electrons when exposed to light

In Na₂ SO₄.10 H₂O. So the metal will be Na (sodium). The salt is washing soda.

Calcium Sulphate (plaster of paris), CaSO₄. 1/2H₂O :
It is a hemihydrate of calcium sulphate. It is obtained when gypsum, CaSO₄ .2H₂O,is heated to 393 K
2(CaSO₄.2H₂O) ⟶ 2CaSO₄,H₂O + 3H₂O
Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO₄ is formed. This is a known 'dead burnt plaster'.
It has a remarkable property of setting with water. on mixing with an adequate quantity of water it forms a plastic mass that gets into hard solid in 5 to 15 minutes.

S.No	Properties
1	Beryllium chloride forms a dimeric structure like aluminium chloride with chloride bridges. Beryllitrm chloride also forms polymeric chain structure ln addition to dinner. Both are soluble in organic solvents and are strong lewis acids.
2	Beryllium hydroxide dissolves in excess of alkali and gives beryllate ion [Be(OH)2]2- as aluminium hydroxide which gives aluminate ion, [Al(OH)4]-
3	Beryllium arid aluminum ions have strong tendency to form complexes,
4	Both beryllium and aluminium hydroxides are amphoteric in nature.
5	Carbides of beryllium (Be2C) like aluminum carbide (Al4C3) give methane on hydrolysis
6	Both beryllium and aluminium are rendered passive by nitric acid

(i) All alkali metals react with hydrogen at about 673K (lithium at 1073K) to form the corresponding hydride which are ionic 10 nature.
(ii) Reactivity of alkali metals with hydrogen increases from Li to Cs
2M + H₂ ⟶ 2M⁺H^- (M= Li,Na,K,Rb,Cs)
(iii) Ionic character of the hydrides increases from Li to Cs.
(iv) The decrease in ionization enthalpy down the group permits easy availability of electrons to hydrogen, forming H⁺ ion.
(v) The hydrides behave as strong reducing agents and their reducing nature increases down the group.

(i) Magnesium and calcium also play a vital role in biological functions. A typical adult human body contains about 25 g of magnesium and 1200 g of calcium. Magnesium plays an important· role in many biochemical reactions catalysed by enzymes. It is the co-factor of all enzymes that utilize ATP in phosphate transfer and energy release. It is also essential for DNA synthesis and is responsible for the stability and proper functioning of DNA.It is also used for balancing electrolytes in our body. Deficiency of magnesium results into convulsion and neuromuscular irritation.
(ii) Calcium is a major component of bones and teeth. It is also present in blood and its concentration is maintained by hormones (calcitonin and parathyroid hormone). Deficiency of calcium in blood causes it to take longer time to clot. It is also important for muscle contraction.
(iii) The main pigment that is responsible for photosynthesis, chlorophyll, contains magnesium which plays an important role in photosynthesis.