Which of the following is used for the dissolution of gold?

What is meant by "water of crystallisation" in a substance? Explain with an example.

$A$ 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.

How is the concentration of a solution expressed in molarity?

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

What happens when metal oxide reacts with water?