Which enzyme becomes active in the stomach during a low $pH$ value?

Which salt solution has a $pH$ greater than $7$?

According to the Bronsted-Lowry acid-base theory,which ion is responsible for the acidity of an aqueous solution of an acid?

Which of the following are present in a dilute aqueous solution of hydrochloric acid?

$A$ sulphate salt of a Group $2$ element of the Periodic Table is a white,soft substance,which can be moulded into different shapes by making its dough. When this compound is left in the open for some time,it becomes a hard solid mass and cannot be used for moulding purposes. Identify the sulphate salt and explain why it shows such behavior. Provide the chemical reaction involved.

Which of the following relations is correct for a basic aqueous solution?