When the radioactive isotope of th-234 emits a beta particle to become pa-234, it also loses a small amount of mass which is emitted as
a) a positron.
b) gamma radiation.
c) an alpha particle.
d) ultraviolet radiation.

b) gamma redaction

Explanation:

Alpha beta and gamma radiations are the examples of ionizing radiations. When an atom is an excited state and having high energy, the atom is in unstable state. The excess of energy is released by the atom to get the stability. The released energy is in the form of radiations which may include alpha, beta, gamma, X-ray etc.

²³⁴Th₉₀ →  + ²³⁴Pa₉₁   + gamma radiation +-1n^0

The gamma radiations are emitted in this reaction.

Gamma radiations:

Gamma radiations are high energy radiations having no mass.

These radiations are travel at the speed of light.

Gamma radiations can penetrate into the many materials.

These radiations are also used to treat the cancer.

Lead is used for the protection  against gamma radiations because of its high molecular density.

The lead apron are used by the person when treated with gamma radiations.

Lead shields are also used in the wall, windows and doors of the room where gamma radiations are treated, in-order to protect the surroundings.

i think   the answer is c hope i'm right