The diagram represents an atom of beryllium (Be) - Edexcel - GCSE Physics - Question 5 - 2012 - Paper 1

The correct symbol for the nucleus of beryllium is D:
egin{array}{c} 9 \ 4 \ Be \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \\ \end{array}

A beryllium atom can become a positive ion by losing one of its electrons.
This process occurs when energy is applied, causing the atom to lose an electron, resulting in a net positive charge due to the excess of positive protons over negative electrons.

During nuclear fusion, two light nuclei combine to form a heavier nucleus.
This process occurs under conditions of extremely high temperature and pressure, such as in the core of the Sun, where hydrogen nuclei fuse to form helium.
The fusion process releases a significant amount of energy, which powers the Sun and produces light and heat.

In nuclear fission, the nucleus of a heavy atom, such as uranium-235, absorbs a neutron and becomes unstable.
This instability causes the nucleus to split into two smaller nuclei, releasing additional neutrons and a large amount of energy in the form of heat.
The released neutrons can initiate further fission reactions in a chain reaction.
In a nuclear reactor, control rods made of materials that absorb neutrons (such as boron or cadmium) are used to regulate the rate of fission.
By adjusting the position of the control rods, the reactor operators can control the number of neutrons available to sustain the fission chain reaction, ensuring safe and efficient energy production.