Question 1

Modern Periodic Law was given by which of the following scientists?

Accepted Answer

Modern Periodic Law was proposed by Henry Moseley in 1913. It states that the physical and chemical properties of elements are periodic functions of their atomic numbers.

Question 2

Which of the following elements has the most negative electron gain enthalpy?

Accepted Answer

Chlorine ($Cl$) has the most negative electron gain enthalpy because Fluorine ($F$) has a very small atomic size, leading to strong inter-electronic repulsions in its compact 2p subshell when an electron is added.

Question 3

Which of the following oxide is amphoteric in nature?

Accepted Answer

Aluminium oxide ($Al2O3$) is amphoteric because it reacts with both acids and bases to form salt and water.

Question 4

Why is the first ionization enthalpy of Nitrogen ($N$) higher than that of Oxygen ($O$)?

Accepted Answer

Nitrogen has electronic configuration $1s^2 2s^2 2p^3$ with half-filled p-orbitals which offer extra stability, making electron removal harder compared to oxygen ($2p^4$).

Question 5

The correct decreasing order of ionic radii for the isoelectronic species $N^{3-}, O^{2-}, F^-$ is:

Accepted Answer

Among isoelectronic species, as nuclear charge ($Z$) increases, ionic radius decreases. $N^{3-} (Z=7) > O^{2-} (Z=8) > F^- (Z=9)$.

Classification of Elements and Periodicity in Properties