iGCSE Chemistry (0620) Core:2.3 Isotopes: Exam Style Questions Paper 1

Question

The symbols represent four atoms. The letters used are not the usual atomic symbols.

\( _{20}^{40}\textrm{W}\) \( _{19}^{40}\textrm{X}\) \( _{20}^{46}\textrm{Y}\) \( _{22}^{46}\textrm{Z}\)

Which atoms are isotopes of the same element?

A) W and X
B) W and Y
C) X and Y
D) Y and Z

▶️ Answer/Explanation

Solution

Ans: B

Isotopes are atoms of the same element (same atomic number) with different mass numbers.

Looking at the given atoms:

Both W and Y have the same atomic number (20) but different mass numbers (40 and 46), making them isotopes of the same element.

X has atomic number 19 (different element), and Z isn’t shown in the given data.

Question

The isotope of which element is used to define the relative atomic mass of other elements?

A) sulfur
B) oxygen
C) nitrogen
D) carbon

▶️ Answer/Explanation

Solution

Ans: D

The standard for atomic masses is based on the carbon-12 isotope (¹²C).

Carbon-12 is defined as having an atomic mass of exactly 12 atomic mass units (amu).

All other elements’ atomic masses are measured relative to 1/12th the mass of a carbon-12 atom.

This standard was adopted because:

Previously, oxygen was used as the standard, but carbon-12 was adopted in 1961 for greater consistency and precision.

An isotope of chromium is represented by \(_{24}^{52}\textrm{Cr}\). Which statement about an atom of this isotope of chromium is correct?

A. It contains 24 electrons.
B. It contains 24 neutrons.
C. It contains 28 protons.
D. It contains 52 neutrons.

▶️Answer/Explanation

Ans:

Isotopes have same atomic number i.e. same number of protons and electrons. Its isotope will also have 24 number of electrons.

Which statement explains why graphite is used as a lubricant?

A All bonds between the atoms are weak.

B It conducts electricity.

C It has a low melting point.

D Layers in the structure can slide over each other.

▶️Answer/Explanation

Ans:D

Layers in the structure can slide over each other hence it is used as a lubricant.

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