Which two particles each have a mass approximately equal to one atomic mass unit?
(1) electron and neutron
(2) electron and positron
(3) proton and electron
(4) proton and neutron

Answer is: (4) proton and neutron.

One unified atomic mass unit is approximately the mass of one nucleon (proton or neutron).

The unified atomic mass unit (amu) is a standard unit of atom mass.  

One unified atomic mass unit is approximately the mass of one nucleon (1.66·10⁻²⁷ kg).

For example, one carbon atom has mass of 12 amu (unified atomic mass).

The electron has a mass that is approximately 1/1836 that of the proton.

Answer : The correct option is, (4) proton and neutron

Explanation :

There are three subatomic particles which are protons, neutrons and electrons.

The protons and the neutrons are present in the nucleus. Protons are positively charged and neutrons has no charge.

The electrons are present around the nucleus or outside the nucleus and electrons are negatively charged.

The mass of proton and neutron is equal to one atomic mass unit.

The mass of electron is zero.

The positron is also a subatomic particle with the same mass of an electron. But the positron are positively charged. That means the mass of positron is also zero.

Hence, the proton and neutron two particles each have a mass approximately equal to one atomic mass unit.