Unit-1 / AS level chemistry- multiple choice questions.

The isotopes of magnesium, ²⁴Mg and ²⁵Mg, both form ions with charge 2+. Which of

the following statements about these ions is true?

• Both ions have electronic configuration 1s² 2s² 2p⁶ 3s²

• 
• The ions have the same number of electrons but different numbers of neutrons.

• The ions have the same number of neutrons but different numbers of protons.

Chlorine has two isotopes with relative isotopic mass 35 and 37. Four m/z values are given below. Which will occur in a mass spectrum of chlorine gas, Cl_2, from an ion with a single positive charge?

• 35.5

• 36

• 71

• 72

The human body contains around 0.025 g of iodine molecules, I_2. Which of the following shows the number of iodine atoms in 0.025 g of I₂?

• 
• 
• 
• 

Which equation represents the reaction for which the enthalpy change, ΔH, is the mean bond enthalpy of the C–H bond?

• ¼CH4(g) → ¼C(g) + H(g)

• CH₄(g) → C(s) + 2H₂(g)

• CH₄(g) → C(g) + 4H(g)

• CH₄(g) → C(g) + 2H₂(g)

The first ionization energies, in kJ mol–1, of four elements with consecutive atomic numbers are shown below.

A 1680

B 2080

C 496

D 738

Which element could be an inert gas?

• A

• B

• C

• D

The graph above shows the second ionization energy of a series of elements with consecutive atomic numbers.

Which element could be lithium?

• A

• B

• C

• D

The first five ionization energies, in kJ mol–1, of aluminium are

578 1817 2745 11 578 14 831

The orbitals from which the first five electrons are removed during ionization, starting with the first electron, are

• 1s 2s 2p 3s 3p

• 1s 1s 2s 2s 2p

• 3p 3s 2p 2s 1s

• 3p 3s 3s 2p 2p

Going across the Periodic Table from sodium to aluminium,

• the melting temperature increases.

• the radius of the atom increases.

• the radius of the metal ion increases.

• the bonding in the element changes from metallic to covalent.

Going down Group 1 from lithium to rubidium

• the radius of the atom decreases.

• the radius of the ion decreases.

• the first ionization energy decreases.

• the polarizing power of the ion increases.

Which of the following mixtures could not form whe octane, C₈H_18, is cracked?

• propane + pentene

• butane + butene

• pentane + propene

• heptane + ethene