iGCSE Chemistry Multiple Choice (Extended) : 2.3 Isotopes: Exam Style Questions Paper 2

Question

Rubidium has two isotopes, \( _{37}^{85}\textrm{Rb}\) and \( _{37}^{87}\textrm{Rb}\).

Which statement explains why both isotopes have the same chemical properties?

A) They have the same number of protons.
B) They have the same electronic configuration.
C) They have different numbers of neutrons.
D) They have different mass numbers.

▶️ Answer/Explanation

Solution

Ans: B

Chemical properties are determined by the arrangement of electrons, which governs how atoms interact with other atoms.

Let’s analyze each option:

A: While true that they have the same protons (37), this alone doesn’t explain chemical properties directly.

B: Correct answer. Isotopes have identical electronic configurations because they have the same number of electrons (equal to protons in neutral atoms), which determines chemical behavior.

C & D: These describe differences between isotopes (neutron number and mass number), but these don’t affect chemical properties.

Key point: Chemical reactions involve electrons, and since isotopes have identical electron arrangements, they behave the same chemically despite different masses.

Question

A sample of iridium has a relative atomic mass of 192.29.

The sample contains two isotopes only.

64.50% of the sample is ¹⁹³Ir.

What is the other isotope in the sample?

A) ¹⁸⁹Ir
B) ¹⁹⁰Ir
C) ¹⁹¹Ir
D) ¹⁹²Ir

▶️ Answer/Explanation

Solution

Ans: C

Let the other isotope be ^xIr. The percentage of this isotope is 100% – 64.50% = 35.50%. The relative atomic mass is the weighted average of the isotopes:

192.29 = (64.50 × 193 + 35.50 × x)/100

Solving for x: 19229 = 12448.5 + 35.5x → 6780.5 = 35.5x → x ≈ 191

Therefore, the other isotope must be ¹⁹¹Ir (option C). The calculation shows that only this value gives the correct weighted average.

Question

Which statement explains why isotopes of the same element have the same chemical properties?

A. They have the same electronic structure.
B. They have the same relative mass.
C. They have the same nucleon number.
D. They have the same proton number.

Answer/Explanation

Ans:

Question

Which statement about the atoms of all the isotopes of carbon is correct?
A They are all radioactive.
B They have the same mass.
C They have the same number of neutrons.
D They have the same number of electrons in the outer shell.

Answer/Explanation

Ans: D

iGCSE Chemistry Multiple Choice (Extended) : 2.3 Isotopes: Exam Style Questions Paper 2

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