Which gas is released when acid reacts with metal?

Which of the following statements is true for acids?

How does the acidity of an acidic aqueous solution change as the concentration of $[H_{3}O^{+}]$ decreases?

Explain why:
$(a)$ the colour of copper sulphate crystals changes on heating?
$(b)$ baking soda acts as an antacid?
$(c)$ an acid should be added to water while diluting?

Which of the following substances enters our body when a red ant bites us?

What is the chemical formula of gypsum?