A substance which gives brick red flame and breaks down on heating to give oxygen and a brown gas is

Which of the following statements is true about $\mathrm{Ca}(\mathrm{OH})_2$ ?

A chemical $A$ is used for the preparation of washing soda to recover ammonia. When $\mathrm{CO}_2$ is bubbled through an aqueous solution of A , the solution turns milky. It is used in white washing due to disinfectant nature. What is the chemical formula of $A$ ?

Dehydration of hydrates of halides of calcium, barium and strontium i.e., $\mathrm{CaCl}_2 \cdot 6 \mathrm{H}_2 \mathrm{O}, \mathrm{BaCl}_2 \cdot 2 \mathrm{H}_2 \mathrm{O}, \mathrm{SrCl}_2 \cdot 2 \mathrm{H}_2 \mathrm{O}$, can be achieved by heating. These become wet on keeping in air. Which of the following statements is correct about these halides?

Metallic elements are described by their standard electrode potential, fusion enthalpy, atomic size, etc. The alkali metals are characterised by which of the following properties?