Match the atoms which might substitute for one another. Match the items in the left column to the items in the right column.
Atoms which might substitute for one another can be found in the same column in the periodic table.
So, since Si and C are found in the same column, they can substitute each other.
1. Si = C
2. K = Na
3. Nb = V
4. Cu = Ag
5. P = As
6. Mg = Ca