AS Level Chemistry chapter 9: The Periodic Table: chemical periodicity MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
68 exam-style questions on The Periodic Table: chemical periodicity, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten The Periodic Table: chemical periodicity questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Why is the radius of the P3− ion much larger than that of the Al3+ ion?
A
P3− has a greater nuclear charge
B
phosphorus is a non-metal
C
Al3+ has more electrons than P3−
D
P3− has three occupied electron shells, while Al3+ has only two
Show answer
Answer: D. Al3+ has lost its third shell (2,8), whereas P3− has gained electrons into it (2,8,8). The extra shell outweighs the larger nuclear charge of phosphorus.
2. Element Y burns brightly in oxygen to form a basic oxide YO, and its chloride YCl2 is an ionic solid with a high melting point. In which group is Y?
A
Group 1
B
Group 14
C
Group 2
D
Group 17
Show answer
Answer: C. The 2+ ion shown by YO and YCl2, combined with ionic compounds and a basic oxide, identifies a reactive metal with two outer electrons: Group 2.
3. Element W forms a chloride WCl4 that is a liquid at room temperature and does NOT react with water, unlike SiCl4. Its dioxide, WO2, is a gas. Where is W in the Periodic Table?
A
Period 2, Group 14
B
Period 3, Group 14
C
Period 2, Group 16
D
Period 3, Group 16
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Answer: A. WCl4 and WO2 fit Group 14. Silicon tetrachloride is hydrolysed, but carbon has no available orbitals in its outer shell to accept a lone pair from water, so CCl4 does not react; CO2 is a gas while SiO2 is a giant covalent solid. W is carbon.
4. Which Period 3 element is the best conductor of electricity?
A
sodium
B
silicon
C
aluminium
D
sulfur
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Answer: C. Conductivity rises from Na to Al because each atom releases more delocalised electrons per ion (one, two, three). Silicon is a semiconductor and sulfur, a molecular solid, does not conduct.
5. Why is aluminium a better electrical conductor than sodium?
A
aluminium atoms are larger
B
aluminium has more delocalised electrons per atom
C
aluminium has a giant covalent structure
D
aluminium ions can move through the solid
Show answer
Answer: B. Each Al atom gives three electrons to the sea of delocalised electrons, Na only one, so aluminium has more mobile charge carriers. The positive ions stay fixed in the lattice.
6. Which of these chlorides is most likely to react with water to give a strongly acidic solution containing HCl?
A
CaCl2
B
KCl
C
AsCl3
D
BaCl2
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Answer: C. Across a period the chlorides change from ionic to covalent. AsCl3, like PCl3, is a covalent chloride that is hydrolysed, releasing HCl. KCl, CaCl2 and BaCl2 are ionic Group 1 and Group 2 chlorides that simply dissolve to give near-neutral solutions.
7. Element Q is a yellow solid that burns with a blue flame to give a colourless, choking gas. The gas dissolves in water to give an acidic solution. What is Q?
A
phosphorus
B
sulfur
C
sodium
D
magnesium
Show answer
Answer: B. S + O2 → SO2. Sulfur is a yellow non-metal; SO2 is a choking gas that forms an acidic solution. Phosphorus burns with a white flame to give a white solid oxide.
8. 3.10 g of white phosphorus is burned in excess oxygen to form P4O10. What mass of oxide is formed? (Ar: P = 31.0)
A
3.55 g
B
7.10 g
C
14.2 g
D
28.4 g
Show answer
Answer: B. P4 + 5O2 → P4O10. n(P) = 3.10/31.0 = 0.100 mol, so n(P4O10) = 0.0250 mol × 284 = 7.10 g. 28.4 g forgets that four P atoms go into each P4O10; 14.2 g uses P2O5 with a 1 : 1 ratio.
9. Element R melts at 44 °C, forms two chlorides, RCl3 and RCl5, and its highest oxide dissolves in water to give a solution of pH about 2. What is R?
A
aluminium
B
silicon
C
phosphorus
D
sulfur
Show answer
Answer: C. A low melting point indicates a simple molecular element, and chlorides showing +3 and +5 together with an acidic oxide point to phosphorus (P4, PCl3, PCl5, P4O10). Sulfur does not form RCl5.
10. Why is the radius of a chloride ion, Cl−, larger than that of a chlorine atom?
A
Cl− has one more electron shell
B
Cl− has a greater nuclear charge
C
Cl− has fewer electrons
D
Cl− has the same nuclear charge but one more electron, so repulsion between the electrons increases
Show answer
Answer: D. Gaining an electron does not add a shell or a proton; the extra electron–electron repulsion with the same nuclear charge makes the outer shell expand.
The Periodic Table: chemical periodicity: questions students ask
How many The Periodic Table: chemical periodicity MCQs are there?
68, each with the answer and a short explanation, across 3 topics: Periodicity of physical properties of the elements in Period 3, Periodicity of chemical properties of the elements in Period 3, Chemical periodicity of other elements. Every chapter test draws ten of them, so you can take it many times.
Is the AS Level Chemistry chapter 9 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
