Question

Identify the correct statements from the following: (a) Alkali metals are strong reducing agents. (b) KO$_2$ is a diamagnetic oxide. (c) Lithium chloride exists as LiCl . 2H$_2$O

• A. a, b only
• B. a, c only
• C. b, c only
• D. a, b, c

Hint:

\textbf{Reducing agents:} Substances that donate electrons (get oxidized). Alkali metals are strong reducing agents.
\textbf{Paramagnetism/Diamagnetism:} Paramagnetic substances have unpaired electrons. Diamagnetic substances have all electrons paired. Use MOT for O$_2^-$. O$_2^-$ has an odd number of valence electrons (13), so it must be paramagnetic. (Actually, it has 1 unpaired electron in a $\pi^*$ MO).
\textbf{Hydration of salts:} Small, highly charged cations (like Li$^+$) have high hydration energies and often form hydrated crystalline salts. LiCl forms LiCl$\cdot$2H$_2$O.

Answer 1

The Correct Option is B

Let's analyze each statement: (a) Alkali metals are strong reducing agents. Alkali metals (Group 1) have one valence electron ($ns^1$). They have a strong tendency to lose this electron to form M$^+$ ions, meaning they are easily oxidized. M $\rightarrow$ M$^+$ + e$^-$ Substances that are easily oxidized act as strong reducing agents (they cause other substances to be reduced). Alkali metals have low ionization enthalpies and highly negative standard reduction potentials (e.g., $E^\ominus (\text{Li}^+/\text{Li}) = -3.05 \text{ V}$), indicating their strong reducing nature. So, statement (a) is correct. (b) KO$_2$ is a diamagnetic oxide. KO$_2$ is potassium superoxide. The superoxide ion is O$_2^-$. The molecular orbital configuration of O$_2^-$ (17 total electrons, or 13 valence electrons if starting from $2s$ orbitals): $(\sigma_{2s})^2 (\sigma^*_{2s})^2 (\sigma_{2p_z})^2 (\pi_{2p_x}, \pi_{2p_y})^4 (\pi^*_{2p_x}, \pi^*_{2p_y})^3$. In the $\pi^*_{2p}$ antibonding orbitals, there are 3 electrons. This means one $\pi^*_{2p}$ orbital is filled with two electrons (paired), and the other $\pi^*_{2p}$ orbital has one unpaired electron. For example: $(\pi^*_{2p_x})^2 (\pi^*_{2p_y})^1$. Due to the presence of this one unpaired electron in the O$_2^-$ ion, KO$_2$ is paramagnetic, not diamagnetic. (Diamagnetic substances have all electrons paired). So, statement (b) is incorrect. (c) Lithium chloride exists as LiCl . 2H$_2$O Lithium ion (Li$^+$) is very small and has a high charge density. Due to this, it has a high hydration enthalpy and tends to form hydrated salts. Lithium chloride indeed crystallizes from aqueous solution as a hydrate, commonly LiCl$\cdot$2H$_2$O. Other alkali metal chlorides (NaCl, KCl, etc.) are generally anhydrous because their cations are larger and have lower charge densities, thus weaker hydration tendencies. So, statement (c) is correct. Based on the analysis: Statement (a) is correct. Statement (b) is incorrect. Statement (c) is correct. Therefore, the correct statements are (a) and (c). This corresponds to option (b). \[ \boxed{\text{a, c only}} \]