For beta radiation, what stops its penetrating abilities?
aluminum

a piece of paper

skin

thin fabric

The correct answer is aluminium.

Beta radiation consists of electrons that are ejected by the nucleus. Beta particles have the charge of an electrons and the mass of an electron.  Beta particles are quite small , giving them the ability to travel through materials a bit longer before collisions with other particles makes them stop hence they can not be stopped by skin, a piece of paper and thin fabric. Their size accounts for why they have more penetration abilities than alpha particles which are large and can be stopped by a thin piece of paper. However, it is known that a few millimeters of aluminium sheet is able to stop beta particles.

The correct answer is aluminium.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)