Em tham khảo nha :
\(\begin{array}{l}
15)\\
1 \le \dfrac{n}{p} \le 1,5 \Rightarrow 1 \le \dfrac{{34 - 2p}}{p} \le 1,5\\
\Rightarrow 9,7 \le p \le 11,6\\
TH1:p = 10\\
n = 34 - 20 = 14\\
A = 10 + 14 = 24\text{(Loại)}\\
TH2:p = 11\\
n = 34 - 22 = 12\\
A = 11 + 12 = 23dvC\text{(Nhận)}\\
X:Natri(Na)\\
18)\\
a)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^5}\\
b)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}\\
c)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^4}\\
d)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^2}\\
e)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^5}\\
f)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}\\
g)\\
1{s^2}2{s^2}2{p^6}3{s^2}3{p^1}
\end{array}\)
