<u>Answer:</u> The correct answer is Option A.
<u>Explanation:</u>
Standard enthalpy of formation is the change in enthalpy of one mole of a substance present at the standard state that is 1 atm of pressure and 298 K of temperature. The substance is formed from its pure elements under the same conditions.
We are given a chemical compound having chemical formula 
This compound is formed by the combination of calcium, nitrogen and oxygen elements.
The chemical equation for the formation of
from the components in their standard states follows:

Hence, the correct answer is Option A.
We can predict the order of the elements given above according from the highest to lowest first ionization energies by using the trends in a periodic table. For elements in a family, the ionization energy decreases as it goes down. Therefore, the correct order would be Be, Mg, Ca, Sr.
Answer:
2K+(aq) + CO3²¯(aq) + Ca^2+(aq) + 2F¯(aq) —› Cu2CO3(s) + 2K+(aq) + 2F¯(aq)
Explanation:
K2CO3(aq) + 2CuF(aq) → Cu2CO3(s) + 2KF(aq)
The complete ionic equation for the above equation can be written as follow:
In solution, K2CO3 and CuF will dissociate as follow:
K2CO3(aq) —› 2K+(aq) + CO3²¯(aq)
CuF(aq) —› Ca^2+(aq) + 2F¯(aq)
Thus, we can write the complete ionic equation for the reaction as shown below:
K2CO3(aq) + 2CuF(aq) —›
2K+(aq) + CO3²¯(aq) + Ca^2+(aq) + 2F¯(aq) —› Cu2CO3(s) + 2K+(aq) + 2F¯(aq)
For the basic solution:
11.2 = -log[H+]
[H+] = 6.31 x 10⁻¹²
For the acidic solution:
2.4 = -log[H+]
[H+] = 3.98 x 10⁻³
The difference:
3.98 x 10⁻³ - 6.31 x 10⁻¹²
≈ 4.0 x 10⁻³
The answer is B