passwella.
Menu

Unilorin Post-UTME Chemistry 2021 (Model questions) past questions and answers

10 questions. Try each one, then open the answer to check yourself and read the explanation.

Question 1

Atomic Structure

How many orbitals are in the d-sub shell?

  1. A.1
  2. B.3
  3. C.5
  4. D.7
Show the answer and explanation

Answer: C (5)

Explanation

s has 1 orbital, p has 3, d has 5 and f has 7.

Open this question

Question 2

Atomic Structure

An element X has isotopic masses of 6 and 7. If the relative abundance is 1 to 12.5 respectively, what is the relative atomic mass of X?

  1. A.6.0
  2. B.6.1
  3. C.6.9
  4. D.7.0
Show the answer and explanation

Answer: C (6.9)

Explanation

Relative atomic mass = (6 × 1 + 7 × 12.5)/(1 + 12.5) = 93.5/13.5 ≈ 6.9.

Open this question

Question 3

Radioactivity

An atom X decays by alpha particle emission to give an atom Y. The atomic number and mass number of Y are

  1. A.90 and 234 respectively
  2. B.91 and 238 respectively
  3. C.92 and 236 respectively
  4. D.93 and 238 respectively
Show the answer and explanation

Answer: A (90 and 234 respectively)

Explanation

Alpha emission removes 2 protons and 4 nucleons. Taking X as uranium-238 (Z = 92), Y has Z = 90 and A = 234; only option A shows a fall of 2 and 4.

Open this question

Question 4

Atomic Structure

An element with mass number 133 and atomic number 55 has

  1. A.55 electrons and 55 neutron
  2. B.55 electrons and 78 neutron
  3. C.78 electrons and 78 neutron
  4. D.78 electrons and 55 neutron
Show the answer and explanation

Answer: B (55 electrons and 78 neutron)

Explanation

A neutral atom has as many electrons as protons (55); neutrons = 133 − 55 = 78.

Open this question

Question 5

Atomic Structure

Which of the following pairs of species contains the same number of electrons? [6C, 8O, 10Ne, 11Na, 12Mg, 13Al, 17Cl]

  1. A.Mg2+ and Al3+
  2. B.Cl− and Ne
  3. C.Na+ and Mg
  4. D.C and O2−
Show the answer and explanation

Answer: A (Mg2+ and Al3+)

Explanation

Mg2+ has 12 − 2 = 10 electrons and Al3+ has 13 − 3 = 10 electrons.

Open this question

Question 6

Atomic Structure

An element X has electronic configuration 1s22s22p63s23p64s2. To which group of the periodic table does X belong?

  1. A.I
  2. B.II
  3. C.III
  4. D.IV
Show the answer and explanation

Answer: B (II)

Explanation

X is 2, 8, 8, 2: two electrons in the outermost shell, so it is in group II (it is calcium).

Open this question

Question 7

Periodic Table

Which of the following sets of elements is arranged in order of increasing first ionization energies?

  1. A.11Na, 3Li, 19K, 37Rb
  2. B.37Rb, 19K, 3Li, 11Na
  3. C.3Li, 19K, 11Na, 37Rb
  4. D.37Rb, 19K, 11Na, 3Li
Show the answer and explanation

Answer: D (37Rb, 19K, 11Na, 3Li)

Explanation

Ionization energy falls down a group, so going up group I from Rb to Li it increases: Rb, K, Na, Li.

Open this question

Question 8

Atomic Structure

Which of the following electronic configurations represent that of a noble gas?

  1. A.2,6,8,2
  2. B.2,8,2
  3. C.2,8
  4. D.2,6
Show the answer and explanation

Answer: C (2,8)

Explanation

2,8 (neon) has a full outer shell of eight electrons, which is typical of noble gases.

Open this question

Question 9

Chemical Bonding

Diamond is a hard substance because its carbon atoms are held by

  1. A.delocalised electrons
  2. B.strong electro static forces
  3. C.Van der Waals forces
  4. D.strong directional covalent bonds.
Show the answer and explanation

Answer: D (strong directional covalent bonds.)

Explanation

Each carbon in diamond is joined to four others by strong covalent bonds in a rigid 3-D network.

Open this question

Question 10

Metals and their Compounds

The presence of unpaired electrons in an atom of a d-block element accounts for its

  1. A.ductility
  2. B.lustre
  3. C.malleability
  4. D.paramagnetism
Show the answer and explanation

Answer: D (paramagnetism)

Explanation

Unpaired d-electrons make a substance attracted into a magnetic field, which is paramagnetism.

Open this question