Radioactivity: Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
A radioactive nucleus consists of an unstable assembly of protons and neutrons which becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
Isotopes: The atoms of an element having the same atomic number but a different mass number are called isotopes. All isotopes have the same chemical properties.
Isobars: The nuclei which have the same mass number (A) but a different atomic number (Z) are called isobars.
EXPLANATION:
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Since the U -238 is an unstable atomic nucleus. The nucleus having an even number of protons and neutrons then that nucleus will be stable.
After splitting into two identical parts it produced two stable nuclei because both have an even number of protons and neutrons. Hence option 2 is correct.