Question

The radioactive decay of uranium into thorium is represented by the equation ${ }_{92}^{238} \mathrm{U} \rightarrow{ }_{90}^{234} \mathrm{Th}+\mathrm{X}$ . The unknown species $X$ is

• A. an electron
• B. a proton
• C. an alpha particle
• D. a neutron

Answer 1

Answer: (C)

The mass number of $X$ must be $238-234=4$ and atomic number of $X$ must be $92-90=2$ .
Hence, $X$ must be an alpha particle.