Chemical A is used for water softening to remove temporary hardness, A reacts with Na2Co3 to generate caustic soda. When CO2 is bubbled through A, it turns cloudy. If the chemical formula of A is \(Ca (OH)_{2} + CO_{2} \rightarrow CaCo_{?} \downarrow + H_{2}O \) then what is the value of ?


In the first configuration (1) as shown in the figure, four identical charges \( q_0 \) are kept at the corners A, B, C and D of square of side length \( a \). In the second configuration (2), the same charges are shifted to mid points C, E, H, and F of the square. If \( K = \frac{1}{4\pi \epsilon_0} \), the difference between the potential energies of configuration (2) and (1) is given by: