iGCSE Chemistry (0620) Core:2.3 Isotopes: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
To find the proton number of each isotope, subtract the number of neutrons from the nucleon number. For W: $35 – 18 = 17$ protons; X: $37 – 20 = 17$ protons; Y: $39 – 20 = 19$ protons; Z: $40 – 22 = 18$ protons. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Since W and X both have 17 protons (but different nucleon numbers), they are isotopes of the same element, making statement A correct. The other statements are incorrect: X and Y have different proton numbers so they are different elements, Y and Z have different proton numbers, and Z has 18 protons while Y has 19, so Z does not have a higher proton number than Y.
▶️ Answer/Explanation
Detailed solution:
$^{11}_{5}\mathrm{B}$ has atomic number 5, so any isotope of boron must have 5 protons. In a neutral atom, electrons equal protons, so 5 electrons. $^{11}_{5}\mathrm{B}$ itself has 11 – 5 = 6 neutrons. The question asks for a particle which is an isotope of $^{11}_{5}\mathrm{B}$. An isotope has the same number of protons (5) but a different number of neutrons. Option A (5 electrons, 5 neutrons, 5 protons) represents boron-10 ($^{10}_{5}\mathrm{B}$), which is indeed a different isotope of boron. Option B represents $^{11}_{5}\mathrm{B}$ itself, while options C and D have the wrong number of protons.
▶️ Answer/Explanation
Detailed solution:
Isotopes are versions of the same element that have an identical number of protons but a different number of neutrons. Since the nucleon number is the sum of protons plus neutrons, a change in the number of neutrons directly changes the nucleon number. The electron arrangement, including the number of shells and outer electrons, stays exactly the same because isotopes of an element have identical chemical properties governed by their matching electronic configurations.