Nobody specifically made the periodic table but it was first thought of by Dmitri Mendeleev in 1869.
Answer:
The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon. The first two, sodium and magnesium, are members of the s-block of the periodic table, while the others are members of the p-block.
Explanation:
Answer:
5
Explanation:
mass number=no of protons +no of neutron
mass number-atomic number=no of neutron
12-7=5
Answer:

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When we have PH = 9.75
So we can get POH = 14 - 9.75 = 4.25
and when POH = - ㏒[OH-]
by substitution:
4.25 = -㏒[OH-]
∴[OH] = 5.6x10^-5
from this reaction equation:
BOH ↔ B+ + OH-
∴[OH-] = [B+]= 5.6x10^-5 M
and Equ [BOH] = 0.5 m - X
= 0.5 - (5.6x10^-5)
= 0.4999
∴ Kb = [OH-][B+]/[BOH]
= (5.6x10^-5)^2 / 0.4999
= 6.27x10^-9