Question

The radioactive decay of uranium into thorium is given by the equation ${}_{92}{U}^{238}\to {}_{90}T{h}^{234}+X,?$

• A. A neutron
• B. An $\alpha$ -particle
• C. Electron
• D. Proton

Answer 1

Answer: (B)

Total atomic number and mass number should be equal to both sides of equation.
Atomic number of $X=92-90=2$
Mass number of $X=238-234=4$
So, element is $X$, hence it is $\alpha$ particle.( Because atomic number of $\alpha$ is 2 and mass number is 4 )