salt.

1.
A is incorrect.
Some salts give acidic solutions. For example, NH4Cl(aq) solution is acidic because of the hydrolysis of NH4+(aq) ion.
NH4+(aq) → NH3(aq) + H+(aq)
Some salts give alkaline solutions. For example, Na2CO3(aq) solution is alkaline because of the hydrolysis of CO32-(aq) ion.
CO32-(aq) + H2O(l) → HCO3-(aq) + OH-(aq)
If you are a CE student, forget the explanation.

B is incorrect.
This is because neutralization of a strong acid with a weak alkali can also give a salt. For example, the neutralization of H2SO4 (a strong acid) and NH3 (a weak alkali) give the salt (NH4)2SO4.
2NH3(aq) + H2SO4(aq) → (NH4)2SO4

C is incorrect.
Salts can be made by methods other than involving an acid. For example, heating NaHCO3 gives a salt, Na2CO3.
2NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g)

D is correct.
For example, NH4Cl has a positive part NH4+ (which derived from NH3) and a negative part Cl- (which derived from HCl).

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2.
NH3 is an alkali.

Among all common gases we know, NH3 gas is the most soluble in water. The solution is alkaline because NH3 can be partly ionized in water to give OH-(aq) ions.
NH3(aq) + H2O(l) = NH4+(aq) + OH-(aq)