Hydrogen fluoride can etch glass - it reacts with the main
component of glass, silicon dioxide, in the following equilibrium
reaction above the boiling point of water:

SiO2(s) + 4 HF(9) = SiF4(g) + 2 H20(g)

Predict whether [SiF4] increases, decreases, or remains
unchanged when:

(a) H2O(g) is removed.
(b) Some steam is added.
(c) Some hydrogen fluoride is removed.
(d) Some silicon dioxide is removed.