Which of the following non-metal elements has half the atomicity of sulfur?

Which type of glass is used in the manufacturing of lenses and prisms?

Assertion: Diamond is a bad conductor.
Reason: Graphite is a good conductor.

In the following reaction,assign the correct category for the underlined atom in the product of complete hydrolysis at $R.T.$:
$H_3\underset{-}{P}O_5 + H_2O \longrightarrow H_3PO_4 + H_2O_2$

$[SiF_6]^{2-}$ is known whereas $[SiCl_6]^{2-}$ is not. Give possible reasons.

The element that shows greater ability to form $p\pi - p\pi$ multiple bonds is