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[1]
a) ¹⁴₇N³⁻
- proton = 7
- elektron = 10
- neutron = 7
b) ⁴⁰₁₈Ar
- proton = 18
- elektron = 18
- neutron = 22
c) ²⁷₁₃Al³⁺
- proton = 13
- elektron = 10
- neutron = 14
d) ²⁴₁₂Mg
- proton = 12
- elektron = 12
- neutron = 12
e) ³⁵₁₇Cl⁻
- proton = 17
- elektron = 18
- neutron = 18

[2]
³⁵₁₇Cl 65% dan ³⁷₁₇Cl 35%
massa rata-rata (Ar) = ..........................?
Ar Cl = (%Cl-35 x mCl-35) + (%Cl-37 x mCl-37)
         = (65/100 x 35) + (35/100 x 37)
         = 22,75 + 12,95
         = 35,7 sma

[3]
Ar = 16,01
¹⁶O = X%
¹⁸O = (100-X)%
Ar = X%.16 + (100-X)%.18
16,01 = (X/100).16 + ((100-X)/100).18
16,01 = 16X/100 + (1800-18X)/100
1601 = 16X + 1800 - 18X
1601 = 1800 - 2X
-2X = 1601 - 1800
X = -199/-2
X = 99,5
jadi, ¹⁶O = 99,5% dan ¹⁸O = (100-99,5)% = 0,5%

[4] ₂₅X (nomor atom = 25)

[5] ₁₆Y (golongan VI A & periode ke-3)

[6] ₁₇Cl : 1s² 2s² 2p⁶ 3s² 3p⁵ (n = 3, l = 1, m = 0, s = -1/2)

[7] ⁴⁵₂₁X²⁺ ,neutron = 24, konfigurasi elektron : : 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

[8] ³²₁₆X²⁻ : 1s² 2s² 2p⁶ 3s² 3p⁶