Which of these is a neutral salt? Na2SO4 NaCN KF (NH4) 2SO4

The answer is indeed Na2SO4 but let me explain why: this salt is a salt of a strong acid (H2SO4) and strong base (NaOH). NaCN is a basic salt. KF is a basic solution because KOH is strong base and HF is not a strong acid. And NH42SO4 is acid. Have in mind the following to determine if something is neutral, basic or acid:

Strong acid + Strong base = neutral salt

Strong acid + Weak base = acidic salt

Weak acid + Strong base = basic salt

Weak acid + Weak base = neutral salt

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That means the correct answer is

A) Na2SO 4