Choose the statement(s) that is/are true about alpha emission.
a. alpha particles are helium nuclei.
b. alpha particles are negative electrons
c. the emission of an alpha particle results in a daughter element two units less in atomic number and four units less in mass number.
d. the emission of an alpha particle results in a daughter element one unit more in atomic number and the same mass number.

The statements a and d are correct or true .

Explanation:

Alpha  particles are doubly charged helium nucleus (He²⁺) and hence they do not have any electrons as both the electrons present in the He atom are ionized .

Alpha particle is represented by  ₂⁴He.

So the alpha particle or doubly charged Helium nucleus only have its available 2 protons along with the 2 neutrons.

So statement a is correct.

An Alpha particles not at all have any electrons so they cannot be negatively charged electrons.

So statement b is incorrect.

Since atomic number of an element= number of protons

mass number=  number of protons + number of neutrons,

Since the alpha particle has 2 protons and 4 neutrons and  hence any atom which would emit an alpha particle would reduce its atomic number by 2 and mass number by 4.

so statement c is correct.

Also statement d is incorrect.