Question

When a particle and its antiparticle unite, the result is
$$A.$$ A heavier particle
$B.$ Two or more smaller particles
$C.$ Photons
$D.$ Partly matter and partly photons

Answer 1

Hint: We will use the concept of particle and antiparticle and their combination. From the basics of atomic physics we know that an anti-particle has the same mass and opposite charge as that of a particle. Reaction between the particle and its antiparticle will also be considered.

Complete step by step answer:
If a particle and antiparticle unite then there is a release of energy and both of them disappear. Generally during this reaction, energy is released in the form of gamma radiation ($\gamma$) that is photon. The total charge of the system is always conserved during the combination process of particle and antiparticle because charges of particle and antiparticle are opposite.
Therefore, whenever a particle and antiparticle unite, the result is a photon.

Additional Information:
There are many theories regarding anti-particles but we will analyse only fundamentals of particles and antiparticles. For example, the antiparticle of an electron is positron which is also known as antielectron and the antiparticle of a proton is called an antiproton. The total charge of the system is always conserved during the combination process of particle and antiparticle as the charges of particle and antiparticle are opposite. We should also know that electrically neutral particles need not be similar to their anti-particles.

Note:
We should take care of the fact that charges of a particle and its antiparticle are opposite in nature but equal in magnitude. Neutral particles are their own anti-particles except neutron which is made up of quarks and antiquarks. Do not get confused between positron and proton. They are different from each other.