Basic strength of the oxides increases in the order $$L{i_2}O < N{a_2}O < {K_2}O < R{b_2}O < C{s_2}O.$$        The increase in basic strength is due to the decrease in $$I.E.$$  and increase in electropositive character.
The melting points of the halides decrease in the order $$NaF > NaCl > NaBr > NaBr > NaI,$$         as the size of the halide ion increases. The decrease in melting point is due to increase in the covalent character with increase in the size of anion according to Fajan's rule.

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Basic strength of oxides increases down the group.

$$LiCl$$  has partly covalent character. Other halides are ionic in nature. Lattice energy decreases with increase of ionic radius of cation, anion being the same. Larger is the lattice energy, the higher will be m. pt. hence $$NaCl$$  will have highest lattice energy.

Calcium bicarbonate exists in the form of solution.

$$Li$$  reacts with water least vigorously due to small size and very high hydration energy.

Superoxides are paramagnetic in nature due to presence of one unpaired electron in $${\pi ^ * }2p\,MO.$$

The low solubility of $$LiF$$  in water is due to its high lattice enthalpy. Smaller $$L{i^ + }$$ ion is stabilised by smaller $${F^ - }$$ ion.

$$N{a_2}C{O_3}$$  does not decompose to form $$N{a_2}O.$$

Lithium does not form peroxide.