Why do scientists sometimes discuss the possibility of silicon as a basic element for life? A. Silicon has an outer shell of electrons that is similar to carbon.
B. Silicon is similar in atomic mass to carbon.
C. Silicon has an inner shell of electrons that is similar to carbon.
D. Silicon is similar in abundance to carbon.

Explanation:

None of the other answers matter but the right answer which A. Silicon has an outer shell of 4. Carbon can connect with 4 elements  because of its outer shell. CH4 is the simplest example. But C2H6 is also possible.

     H   H

H - C - C - H

     H   H

There are 4 connections to the outside world for the Carbon (C) on the left.

It has 3 hydrogens connected on to it and one of its connecting electrons goes with the other carbon on the right.

Silicon can do the same thing.

option number c is the right answer.