The S Block Elements

Step 1: Analyze statement (A) - Carbonates of Alkaline Earth Metals.
The carbonates of alkaline earth metals (Group 2, ) are generally insoluble in water. The solubility decreases down the group ( is slightly soluble, but are insoluble). The statement is generally accepted as correct in the context of general chemistry.

Step 2: Analyze statement (B) - Beryllium Halides.
Beryllium (Be) is the first and smallest element of Group 2. Due to its very small size and high polarizing power, the compounds it forms, such as its halides ( , etc.), have significant covalent character. exists as a polymeric chain in the solid state, consistent with covalent bonding. The statement is correct.

Step 3: Analyze statement (C) - Superoxides of Alkali Metals.
Alkali metals (Group 1) form superoxides, (e.g., ). Superoxides contain the superoxide ion ( ), which has one unpaired electron. This unpaired electron makes the superoxides paramagnetic and colored (usually yellow or orange).
For example, Potassium superoxide ( ) is a pale yellow solid.
The statement "The super oxides of alkali metals are colourless" is incorrect.

Step 4: Analyze statement (D) - Enthalpies of Formation of Alkali Metal Halides.
Alkali metal halides ( ) are typical ionic compounds formed by the combination of a highly electropositive metal (Group 1) and a highly electronegative non-metal (Group 17).
The formation of these compounds is highly exothermic, driven by the large negative lattice energy of the resulting ionic crystal. This results in a very high negative enthalpy of formation. The statement is correct.

Step 5: Conclude the final answer.
The incorrect statement is (C).

Step 1: Understand the meaning of negative standard potential.
The standard potential value here refers to the standard reduction potential, (for the half-reaction ).
A highly negative indicates a strong tendency for the metal to undergo oxidation ( ), meaning the metal is a strong reducing agent.
The question asks for the order of negative values, so we are looking for the order of strength of the reducing agent.

Step 2: Analyze the factors determining the standard reduction potential for Alkali Metals.
The process of hydration of a metal ion is highly exothermic for small ions (high charge density). The overall process for reduction is: The standard potential is determined by the sum of these energy changes. For alkali metals, the trend is governed by the exceptionally high magnitude of the hydration enthalpy ( ) for the smallest ion, .

Step 3: Compare the reduction potentials of .}
The standard reduction potentials are (in Volts): . . .
The order of the actual potential values is .

Step 4: Determine the order of negative standard potential values.
The negative standard potential values are the magnitudes of these numbers: , , .
The order of negative standard potential values is .
This is because is the strongest reducing agent among the three due to the extremely high hydration energy of the small ion, which makes its reduction potential the most negative.