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