Radioactive decay is the loss of energy by unstable atomic nuclei. The reaction shows alpha decay. Thus, option d is correct.
Alpha decay is a type of radioactive decay in which an alpha particle or the helium ion is released from the parent cell to produce the daughter nucleus.
The alpha decay in the isotope of the uranium to thorium and an alpha particle is shown as:
²³⁵U₉₂ → ²³¹Th₉₀ + ⁴He₂
In beta decay, a negatively charged electron is emitted along with the daughter nucleus and in gamma decay, gamma rays without charge and mass are emitted.
Therefore, the reaction shows option d. alpha decay.
Learn more about alpha decay here:
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