Consider the following statements
I. The radius of an anion is larger than that of the parent atom.
II. The ionisation energy generally increases with increasing atomic number in a period.
III. The electronegativity of elements increases on moving down across a group.
Which of the above statements is/are correct?
A. I alone
B. II alone
C. I and II
D. II and III

Hint: Atomic radius or atomic radii is the total distance present between the central nucleus to the valence orbital of the electrons. Ionisation energy is defined as the amount of energy needed to remove the electrons from its atom or ion.Electronegativity is the property of an atom to attract electrons toward itself.

Complete step by step solution:
As we move down in the group, the size of the neutral atom increases whereas it decreases as we move across the period.
The atomic size increases or decreases due to the formation of anion and cation.
The anion is formed by gaining electrons whereas a cation is formed by the loss of electrons.

Having a look at the given statements:
I. In anion, as there is an increase in the number of electrons, the number of protons remains the same. The extra electron is present in the outermost orbital which increases the electron-electron repulsion, the proton cannot keep the extra electrons tightly bonded to the nucleus which results in the decrease of the effective nuclear charge of the electron and thus the size of the anion is larger than the neutral atom.
Thus the statement is correct.

II. Ionisation energy is related to the atomic radius trend. It increases on moving left to right in the period as the atomic radius decreases across the period which results in highly effective attraction in electrons. As the size decreases, the atomic number increases. Therefore, ionisation energy increases as the atomic number increases.
Thus the statement is correct.

III. The electronegative value of an atom increases on moving left to right in a period and decreases moving down in the group.
Thus the statement is incorrect.
Therefore, option (C) is correct.

Note: Noble gases possess a complete valence shell. Therefore, they cannot attract any electrons and do not carry any electronegativity value.