Which of the following forms cyclic silicones on hydrolysis?

Polyphosphates are used as water softening agents because they .......

Identify the incorrect statement about silica $(SiO_2)$.

Diamond and emerald are forms of which of the following respectively?

Assertion : Silicones are hydrophobic in nature.
Reason : $Si-O-Si$ linkages are moisture sensitive.

Reaction of $NaCl$ with conc. $H_2SO_4$ liberates a gas,$X$ that turns moist blue litmus paper red. When gas $X$ is passed into a test tube containing egg shell powder suspended in water,another gas,$Y$ is generated which when passed through lime water makes it milky. The gases $X$ and $Y$,respectively,are