Count protons, neutrons and electrons from mass number and atomic number

1. A.
   $^{40}_{18}\text{X}$
2. B.
   $^{40}_{19}\text{X}$
3. C.
   $^{40}_{12}\text{X}$
4. D.
   $^{40}_{20}\text{X}$

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1. A.
   (A) - (I), (B) - (II), (C) - (III), (D) - (IV)
2. B.
   (A) - (II), (B) - (IV), (C) - (I), (D) - (III)
3. C.
   (A) - (I), (B) - (II), (C) - (IV), (D) - (III)
4. D.
   (A) - (III), (B) - (IV), (C) - (I), (D) - (II)

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1. A.
   $1$
2. B.
   $3$
3. C.
   $2$
4. D.
   $0$

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1. A.
   $15, 15$ and $16$.
2. B.
   $16, 15$ and $15$.
3. C.
   $15, 18$ and $16$.
4. D.
   $16, 15$ and $18$.

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