<u>Answer:</u> The element having similar chemical properties that of calcium present in period 3 is magnesium.
<u>Explanation:</u>
In a periodic table, elements are arranged in 18 vertical columns known as groups and 7 horizontal rows known as periods.
Elements arranged in a group show similar chemical properties because of the presence of same number of valence electrons.
We are given:
Calcium is the 20th element of the periodic table having electronic configuration 
It has 2 valence electrons.
The element present in period 3 and have the same number of valence electron or in the same group is magnesium.
Hence, the element having similar chemical properties that of calcium present in period 3 is magnesium.
Answer: The pH of 0.10 M 
is 4.49.
Explanation:
Given: Initial concentration of 
= 0.10 M
Let us assume that amount of dissociates is x. So, ICE table for dissociation of is as follows.
![Cu(H_{2}O)^{2+}_{6} \rightleftharpoons [Cu(H_{2}O)_{5}(OH)]^{+} + H_{3}O^{+}](https://tex.z-dn.net/?f=Cu%28H_%7B2%7DO%29%5E%7B2%2B%7D_%7B6%7D%20%5Crightleftharpoons%20%5BCu%28H_%7B2%7DO%29_%7B5%7D%28OH%29%5D%5E%7B%2B%7D%20%2B%20H_%7B3%7DO%5E%7B%2B%7D)
Initial: 0.10 M 0 0
Change: -x +x +x
Equilibrium: (0.10 - x) M x x
As the value of 
is very small. So, it is assumed that the compound will dissociate very less. Hence, x << 0.10 M.
And, (0.10 - x) will be approximately equal to 0.10 M.
The expression for value is as follows.
![K_{a} = \frac{[Cu(H_{2}O)^{2+}_{6}][H_{3}O^{+}]}{[Cu(H_{2}O)^{2+}_{6}]}\\1.0 \times 10^{-8} = \frac{x \times x}{0.10}\\x = 3.2 \times 10^{-5}](https://tex.z-dn.net/?f=K_%7Ba%7D%20%3D%20%5Cfrac%7B%5BCu%28H_%7B2%7DO%29%5E%7B2%2B%7D_%7B6%7D%5D%5BH_%7B3%7DO%5E%7B%2B%7D%5D%7D%7B%5BCu%28H_%7B2%7DO%29%5E%7B2%2B%7D_%7B6%7D%5D%7D%5C%5C1.0%20%5Ctimes%2010%5E%7B-8%7D%20%3D%20%5Cfrac%7Bx%20%5Ctimes%20x%7D%7B0.10%7D%5C%5Cx%20%3D%203.2%20%5Ctimes%2010%5E%7B-5%7D)
Hence, ![[H_{3}O^{+}] = 3.2 \times 10^{-5}](https://tex.z-dn.net/?f=%5BH_%7B3%7DO%5E%7B%2B%7D%5D%20%3D%203.2%20%5Ctimes%2010%5E%7B-5%7D)
Formula to calculate pH is as follows.
![pH = -log [H^{+}]](https://tex.z-dn.net/?f=pH%20%3D%20-log%20%5BH%5E%7B%2B%7D%5D)
Substitute the values into above formula as follows.
![pH = -log [H^{+}]\\= - log (3.2 \times 10^{-5})\\= 4.49](https://tex.z-dn.net/?f=pH%20%3D%20-log%20%5BH%5E%7B%2B%7D%5D%5C%5C%3D%20-%20log%20%283.2%20%5Ctimes%2010%5E%7B-5%7D%29%5C%5C%3D%204.49)
Thus, we can conclude that the pH of 0.10 M is 4.49.
It depends on the system if there are more moles of gas on the left and you increase the pressure the yield of a product will increase as the equilibrium moves to the side with the fewest gas molecules
if the right hand side has more moles of gas and you increase the pressure the yield will decrease as the equilibrium shifts to the left hand side where there are more gas moles
hope that helps
I’m pretty sure A. if not i’m sorry
