Chemistry MCQs for NEET — Practice Questions with Answers

For atomic number Z = 34, the element is Selenium (Se), which belongs to the Chalcogen group. For atomic number Z = 37, the element is Rubidium (Rb), which is a representative element. Hence, the correct answer is 'Chalcogen & representative.'

The size of an ion is influenced by its nuclear charge and the number of electrons. The correct order of decreasing atomic size is $ S ^ {2-} ightarrow Cl ^ {-} ightarrow Ar ightarrow K ^ {+} ightarrow Ca ^ {2+} $ because as the nuclear charge increases and the number of electrons decreases, the atomic size decreases.

The reaction $ O ightarrow O ^ {2-} $ requires maximum energy because adding two electrons to oxygen to form $ O ^ {2-} $ involves overcoming a significant amount of electron-electron repulsion within the same orbital, making this process require more energy compared to the others.

The electronegativity of elements generally increases across a period and decreases down a group. Therefore, the order of increasing electronegativity is Si (Silicon), P (Phosphorus), C (Carbon), N (Nitrogen).

The ion $[Co(NH_3)_6]^{3+}$ is diamagnetic because cobalt in this complex is in the +3 oxidation state, which means it has an electronic configuration of $[Ar] 3d^6$. The ammonia ligands are strong field ligands, which cause pairing of all the electrons in the 3d orbitals, resulting in no unpaired electrons.

The compound $[CrCl_2(H_2O)_4]Cl.2H_2O$ is the most likely structure because when 1/3 of the total chlorine is precipitated, it suggests that one out of the three chlorine atoms is outside the coordination sphere and hence can react with $AgNO_3$ to form a precipitate of $AgCl$.