Valency is the number of hydrogen atoms that can combine with an atom of an element to form a molecule. Here are the valencies for the given elements:

Cr (Chromium) - Valency: 6O (Oxygen) - Valency: 2H (Hydrogen) - Valency: 1S (Sulfur) - Valency: 2Si (Silicon) - Valency: 4K (Potassium) - Valency: 1Al (Aluminum) - Valency: 3