Which of the following elements exists in the solid state at $25\,^oC$ temperature and atmospheric pressure?

Gas $A$ is bubbled through slaked lime when a white precipitate is formed. On prolonged bubbling,the precipitate is dissolved. On heating the resultant solution,the white precipitate reappears with the evolution of gas $B$. The gases $A$ and $B$ respectively are

Which fibrous mineral substance can withstand red-hot temperatures without being damaged?

Mark the gas which turns lime water milky.

Which of the following elements has the lowest melting point?

Assertion $(A)$: The maximum covalency of $Si$ and $Ge$ is $6$ but that of carbon is $4$.
Reason $(R)$: Due to the presence of $d$-orbitals in $Si$ and $Ge$,both these elements can undergo $sp^3d^2$ hybridisation and covalency of $6$ is possible. Carbon has no $d$-orbitals in it and hence its covalency is $4$.
The correct answer is: