Which rule for assigning oxidation numbers is correct?

Hydrogen is usually -1.
Oxygen is usually -2.
A pure group 1 element is +1.
A monatomic ion is 0.

Particle model to predict what will happen if a sharp object creates a hole in the soccer ball

Find the number of grams of hcl needed to react completely with .50 moles of magnesium.

Most materials are not magnetic because their magnetism has worn off. their magnetic domains are arranged randomly. they lack magnetic fields. earth’s heat has destroyed their magnetism.