a) The isotope of carbon containing $7$ neutrons has natural abundance of $1.1\%$. This statement is correct because the ${}_6{}^{13}\mathrm{C}$ has the natural abundance of $1.1\%$.
b) Among the IV A group elements, Sn has the lowest melting point. This statement is correct because the melting point decreases down the group.
c) Silicon is the $2^{\mathrm{nd}}$ (by mass) most abundant element in the earth's crust. This statement is correct because it has the $27.7\%$ of earth crust.
d) Elemental carbon shows the highest electrical resistivity among the $14$ group elements. This statement is correct because the graphite has the low resistivity and higher conductivity.

Hence, all the statements are correct.