Number of proton K=19
so, 42 - 19 =23
then the answer in 19 protons and 23 neutrons
Answer : The equilibrium concentration of
in the trial solution is 
Explanation :
First we have to calculate the initial moles of
and
.

and,

The given balanced chemical reaction is,

Since 1 mole of
reacts with 1 mole of
to give 1 mole of 
The limiting reagent is, 
So, the number of moles of
= 0.0020 mmole
Now we have to calculate the concentration of
.

Using Beer-Lambert's law :
where,
A = absorbance of solution
C = concentration of solution
l = path length
= molar absorptivity coefficient
and l are same for stock solution and dilute solution. So,

For trial solution:
The equilibrium concentration of
is,
![[SCN^-]_{eqm}=[SCN^-]_{initial}-[FeSCN^{2+}]](https://tex.z-dn.net/?f=%5BSCN%5E-%5D_%7Beqm%7D%3D%5BSCN%5E-%5D_%7Binitial%7D-%5BFeSCN%5E%7B2%2B%7D%5D)
= 0.00050 M
Now calculate the
.

Now calculate the concentration of
.
![[SCN^-]_{eqm}=[SCN^-]_{initial}-[FeSCN^{2+}]](https://tex.z-dn.net/?f=%5BSCN%5E-%5D_%7Beqm%7D%3D%5BSCN%5E-%5D_%7Binitial%7D-%5BFeSCN%5E%7B2%2B%7D%5D)
![[SCN^-]_{eqm}=(0.00050M)-(9.17\times 10^{-5}M)](https://tex.z-dn.net/?f=%5BSCN%5E-%5D_%7Beqm%7D%3D%280.00050M%29-%289.17%5Ctimes%2010%5E%7B-5%7DM%29)
![[SCN^-]_{eqm}=4.58\times 10^{-8}M](https://tex.z-dn.net/?f=%5BSCN%5E-%5D_%7Beqm%7D%3D4.58%5Ctimes%2010%5E%7B-8%7DM)
Therefore, the equilibrium concentration of
in the trial solution is 
Answer:
Below are the statements which are true about the structure of the periodic table:
B: The inner transition elements are placed at the bottom of the periodic table for easy viewing.
D: The distribution of electrons in energy levels is responsible for the shape of the periodic table.
Explanation:
Point A:
As we know that in a periodic table there are 7 period s and 18 groups. So, the number of periods is evidently lesser than the number of groups. But the shape of periodic table is regular and rectangular so point A is false.
Point B:
The inner transition elements or -f block elements are put at the bottom for easy viewing. These are the elements that have the valence electrons only in the f-orbital's. Therefore, they are placed separately at the bottom side of the table so that they can be easily viewed or studied from there. So, point B is true.
Point C:
If we talk about option C, then it is very clear and true that considering a rectangular shape of the periodic table, the groups are vertically arranged and periods are horizontally arranged, therefore it is false.
Point D:
Atoms of all elements have definite electronic distribution in different energy levels like s, p d or f. This is a very prominent feature of periodic tale that elements are divided in specific blocks, s, p, d and f based on their electronic configurations. Therefore, it is true.
Point E:
We also know that no. of metals in a periodic table are more than the no. of non metals like almost 91 out of 118 elements are metals in periodic table. Therefore, the point E "Nonmetals take up more than half the area of the periodic table." is false.
Hope it helps!
The answer is 303 K, to find K you have to add 273 to the °C