Explanation:
a.
P. When potassium reacts with hydrochloric acid, the salt produced is potassium chloride and sulphur-di-oxide gas is evolved after performing these.
Q.Addition of acid with metal gives salt and hydrogen gas. When dilute Hydrochloric acid is added to iron filings, so chloride & hydrogen gas is produced.
R. and if you talk about gold, gold do not react easily with HCL
b.
# in ascending order P -> Q -> R
c.
# I think its potassium chloride reaction.
hope this helps you
have a great day :)
