since only the ends of magnet are seats of a magnetic strength (ora poles), why do we not save a lot of iron by making a magnet hollow ?

They are all decomposition reactions.

Fine out you self hx

Answeropposite;

Those are different gas lawshere is a brief description of themcharles's law states that volume and temperature are directly proportional to each other as long as pressure is held constant.  boyle's law asserts that pressure and volume are inversely proportional to each other at fixed temperature.gay-lussac's law introduces a direct proportionality between temperature and pressure as long as it is at a constant volume.    source: