Classification of elements and Periodicity in properties MCQs for NEET — Chemistry Questions with Answers

Argon (Ar) is a noble gas with a completely filled valence shell, making it very stable and not inclined to gain any electrons. Thus, it has zero electron gain enthalpy. Lithium (Li), Calcium (Ca), and Fluorine (F) do not have zero electron gain enthalpy as they can gain electrons to achieve a stable configuration.

The element with atomic number 44 is Ruthenium (Ru), which belongs to the d-block of the periodic table. Elements in the d-block are also known as transition metals.

The electronic configuration $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$ corresponds to a noble gas core configuration with one electron in the 4s orbital. The first ionization energy removes this 4s electron, which is relatively easy. However, the second ionization energy requires removing an electron from the stable, noble gas core, which is significantly more difficult. This results in a high difference between the first and second ionization enthalpies.

Noble gases have the highest ionization enthalpy in a period because they have completely filled valence shells, making them very stable and requiring a significant amount of energy to remove an electron. Therefore, option o3 is correct.

The Ga^3+ ion is the most stable because it attains a stable electron configuration similar to that of a noble gas. Despite the high energy required to remove the third electron, the resulting stability of the Ga^3+ ion compensates for this energy loss. Therefore, option o4 is correct.

The incorrect order in the given options is $Bond ext{ }enthalpy ext{ }F_2 ext{ } > ext{ } Cl_2 ext{ } > ext{ } Br_2$. The correct order of bond enthalpy is $Cl_2 > Br_2 > F_2$. This is because the F-F bond is unusually weak due to the high repulsion between the lone pairs of electrons on the fluorine atoms, despite the small size of the fluorine atom.