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CIE iGCSE Co-Ordinated Science C2.3 Isotopes Exam Style Questions Paper 1

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Question

One atom of an isotope of fluorine is represented by \( ^{15}_{9}\text{F} \).

How many neutrons does this atom have?

A. 6
B. 9
C. 10
D. 15

▶️ Answer/Explanation

In the nuclide notation \( ^{A}_{Z}\text{X} \):

  • The top number (A) is the nucleon number (mass number), which is the total number of protons and neutrons in the nucleus.
  • The bottom number (Z) is the proton number (atomic number), which is the number of protons in the nucleus.

For \( ^{15}_{9}\text{F} \):

  • Nucleon number = 15
  • Proton number = 9

The number of neutrons is found by subtracting the proton number from the nucleon number:

\(\text{Number of neutrons} = 15 – 9 = 6\)

Therefore, this atom of fluorine has 6 neutrons. Option A is correct.

✅ Answer: (A)

Question

Which statement about isotopes of the same element is correct?

A. They have the same number of protons but different number of electrons.
B. They have the same number of protons but different number of neutrons.
C. They have the same number of neutrons but different number of electrons.
D. They have the same number of neutrons but different number of protons.

▶️ Answer/Explanation
Isotopes are atoms of the same element, so they must have identical proton (and electron) numbers.
They differ only in the number of neutrons in the nucleus, giving them different mass numbers.
Any statement suggesting differing proton or electron numbers cannot describe isotopes of the same element.
✅ Answer: (B)

Question

X and Y are isotopes of the same element.

Which statement about X and Y is correct?

A. They have the same nucleon number but different numbers of protons.
B. They have the same number of neutrons but different numbers of electrons.
C. They have the same atomic number but different numbers of electrons.
D. They have the same number of protons but different numbers of neutrons.

▶️ Answer/Explanation
Isotopes are atoms of the same element with the same number of protons (same atomic number).
Because they are neutral atoms of the same element, they also have the same number of electrons.
Isotopes differ only in the number of neutrons, and therefore in nucleon (mass) number.
✅ Answer: (D)

Question

The diagrams represent pairs of nuclei of some atoms.

Which pair shows nuclei of different isotopes of the same element?

▶️ Answer/Explanation
Isotopes must have the same number of protons (same element) but different numbers of neutrons.
Option B is the pair where both nuclei have identical proton counts but differing neutron counts.
✅ Answer: (B)

Question

How many neutrons are in one atom of the isotope $_{17}^{35}\textrm{Cl}$ ?

(A)  17

(B)  18

(C)  35

(D  52

▶️Answer/Explanation

Ans: B

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