The molarity of a solution : 0.4 M
<h3>Further explanation</h3>
Given
0.2 moles of Potassium Oxide
500 ml of water = 0.5 L
Required
The molarity
Solution
Molarity is a way to express the concentration of the solution
Molarity shows the number of moles of solute in every 1 liter of solution or mmol in each ml of solution

Assume volume of solution = volume of water(addition of solution volume from volume Potassium Oxide is negligible
Input the value :
M = 0.2 : 0.5
M = 0.4
Answer:
It is A) Calcium
Explanation:
Calcium has an electronic configuration of 2,8,8,2
Answer : The value of acid dissociation constant is, 
Solution : Given,
Concentration pyridinecarboxylic acid = 0.78 M
pH = 2.53
First we have to calculate the hydrogen ion concentration.
![pH=-\log [H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%20%5BH%5E%2B%5D)
![2.53=-\log [H^+]](https://tex.z-dn.net/?f=2.53%3D-%5Clog%20%5BH%5E%2B%5D)
![[H^+]=2.95\times 106{-3}M](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D2.95%5Ctimes%20106%7B-3%7DM)
Now we have to calculate the acid dissociation constant.
The equilibrium reaction for dissociation of (weak acid) is,

initially conc. 0.78 0 0
At eqm. (0.78-x) x x
The expression of acid dissociation constant for acid is:
![k_a=\frac{[C_6H_4NO_2^-][H^+]}{[C_6H_4NO_2]}](https://tex.z-dn.net/?f=k_a%3D%5Cfrac%7B%5BC_6H_4NO_2%5E-%5D%5BH%5E%2B%5D%7D%7B%5BC_6H_4NO_2%5D%7D)
As, ![[H^+]=[C_6H_4NO_2^-]=x](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D%5BC_6H_4NO_2%5E-%5D%3Dx)
So, 
Now put all the given values in this formula ,we get:



Therefore, the value of acid dissociation constant is, 
Answer:
A. 19
B. 40
C. - 1
Explanation: Please see attachment for explanation
The answer is B. scavenger