Question

1. the dense, central core of the atom containing protons and neutrons is the _________.
2. the total number of protons and neutrons in an atom is the _________.
3. a type of particle consisting of two protons and two neutrons (essentially a helium nucleus) is called an _________.

Explanation:

1. By definition, the dense, central core of an atom with protons and neutrons is the nucleus.
2. The sum of protons and neutrons in an atom gives the mass - number.
3. A particle with two protons and two neutrons (like a helium nucleus) released from an unstable nucleus is an alpha - particle.

Answer:

1. nucleus
2. mass - number
3. alpha - particle