26
32
20
14
Answer is Right!
Answer is Wrong!
The correct answer is $\boxed{\text{D}}$, 14.
A homogeneous series is a group of elements that have the same number of protons in their nucleus, but different numbers of neutrons. The difference between the atomic mass units of subsequent members of a homogeneous series is equal to the mass of a neutron.
For example, the first two elements in the homogeneous series of carbon are carbon-12 and carbon-13. Carbon-12 has 6 protons and 6 neutrons, while carbon-13 has 6 protons and 7 neutrons. The difference between their atomic mass units is 1, which is the mass of a neutron.
The other options are incorrect because they do not represent the difference between the atomic mass units of subsequent members of a homogeneous series.