Which of the following salts is formed by the neutralization of a weak acid and a strong base?

According to the $Brønsted-Lowry$ theory, what kind of substance is a base?

Which of the following salts does not contain water of crystallisation?

Which of the following metals reacts with sodium hydroxide to produce a salt and $H_2$ gas?

At which value of $pH$ of the inner side of the mouth does the decay of teeth take place?

In the following schematic diagram for the preparation of hydrogen gas as shown in the Figure,what would happen if the following changes are made?
$(a)$ In place of zinc granules,the same amount of zinc dust is taken in the test tube.
$(b)$ Instead of dilute sulphuric acid,dilute hydrochloric acid is taken.
$(c)$ In place of zinc,copper turnings are taken.
$(d)$ Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.