Carborundum is obtained when silica is heated at high temperature with

Which of the following statements are correct?
$(a)$ The isotope of carbon containing $7$ neutrons has natural abundance of $1.1 \%$.
$(b)$ Among the $IV$ $A$ group elements, $Sn$ has the lowest melting point.
$(c)$ Silicon is the $2^{nd}$ (by mass) most abundant element in the earth's crust.
$(d)$ Elemental carbon shows the highest electrical resistivity among the $14$ group elements.

$Si$ reacts with $CH_3Cl$ at $573 \ K$ in the presence of $Cu$ powder to form methyl substituted chlorosilanes. Among the given methyl substituted chlorosilanes, whose yield is minimum?

$A$ gas that cannot be collected over water is

Ions consisting of two or more atoms which have properties similar to halide ions and contain at least one nitrogen atom are called ........

Carbon can form $p\pi-p\pi$ bond with which kind of elements?