[Froob]

Mendeleev knew that silicon tetrachloride (SiCl4) existed. Using his periodic table, he correctly predicted the existence of "ekasilicon", an element one place below silicon in the periodic table. Use your periodic table to write the formula for the compound formed by Mendeleev's "ekasilicon" and chlorine.

[constant thinker]

This will help you out a lot.

Just do what the question says. It's unbelievably easy. Just use the element "on place below silicon."