Which particles determine the mass of an atom ?

Name the particles which actually determine the mass of an atom.

._92U^238 decays by emitting successively 8 alpha -particles and 8 beta -particles. Determine the mass number and atomic number of the new element and express it in symbol.

Particle 1 experiences a perfectly collision with a staionary particle 2 . Determine their mass ratio , if the particles move perpendicularly to each other.

If uranium (mass number 238 and atomic number 92) emits an alpha-particle, the product has mass no. and atomic no.

How do we determine the atomic mass of an element with its isotopes?