Free s-Block and p-Block Elements MCQs with Answers

11. In group IV, the stability of the plus 2 oxidation state relative to the plus 4 state

• A. decreases down the group
• B. is the same throughout
• C. is zero for all members
• D. increases down the group, so lead two compounds are more stable than lead four

Explanation: This is the inert pair effect: the two s electrons of the outer shell become progressively harder to involve in bonding as the group is descended, so tin favours plus 4 while lead favours plus 2. It follows that lead four compounds such as PbO2 are strong oxidising agents, readily reverting to lead two. The same effect appears in groups III and V.

12. The block of the periodic table to which an element belongs is decided by

• A. the number of shells it has
• B. its atomic mass
• C. the subshell that receives the last electron added
• D. whether it is a metal or a non metal

Explanation: Elements are assigned to the s, p, d or f block according to the subshell into which the differentiating electron enters, so groups I and II form the s block and groups III to VIII the p block. This classification explains why elements in the same block share broad chemical behaviour. Period number, by contrast, is given by the number of the outermost shell.

13. An element with the electronic configuration 1s2 2s2 2p6 3s2 3p4 belongs to

• A. group VI of the p block, period 3
• B. group IV of the p block, period 3
• C. group II of the s block, period 3
• D. group VI of the d block, period 4

Explanation: The outermost shell is the third, giving period 3, and it contains six electrons in total across 3s and 3p, giving group VI, while the last electron entered a p subshell so the element is in the p block. The element is sulphur. Counting only the p electrons and answering group IV is the standard error.

14. Across a period, the first ionisation energy generally

• A. decreases, because atomic size increases
• B. increases, because the atoms get smaller and the nuclear charge increases
• C. remains constant
• D. decreases, because shielding increases sharply

Explanation: A greater nuclear charge acting on a shell at nearly constant distance holds the outer electrons more tightly, so more energy is needed to remove one. The trend is not perfectly smooth, dipping at boron and at oxygen because of the start of the p subshell and the first pairing of p electrons respectively. Those small irregularities are themselves strong evidence for subshell structure.

15. The oxides of the elements across period 3, from sodium to sulphur, change from

• A. acidic through amphoteric to basic
• B. acidic to neutral only
• C. basic through amphoteric to acidic
• D. neutral to basic

Explanation: Sodium and magnesium oxides are basic, aluminium oxide is amphoteric and reacts with both acids and alkalis, and the oxides of phosphorus and sulphur are acidic, dissolving to give acids. The change follows the shift from metallic to non metallic character across the period. Identifying aluminium oxide as the amphoteric turning point is the key fact.

16. Lithium shows a diagonal relationship with

• A. sodium
• B. magnesium
• C. beryllium
• D. aluminium

Explanation: Lithium resembles magnesium because their ions have similar size to charge ratios, so both form nitrides directly with nitrogen, both give carbonates that decompose on heating and both have oxides that are less soluble than those of their own group. Beryllium is diagonally related to aluminium in the same way. Diagonal relationships are strongest in the second and third periods.

17. When calcium reacts with cold water, the products are

• A. calcium oxide and hydrogen
• B. calcium hydride and oxygen
• C. calcium hydroxide and hydrogen
• D. calcium carbonate and hydrogen

Explanation: Calcium reacts steadily with cold water to give a suspension of slightly soluble calcium hydroxide, known as limewater when filtered, together with bubbles of hydrogen. Magnesium reacts only very slowly with cold water but readily with steam, which gives the oxide instead. Calcium carbonate would require carbon dioxide to be present.

18. The flame colour produced by potassium compounds is

• A. golden yellow
• B. brick red
• C. apple green
• D. lilac

Explanation: Heating excites the outer electron to a higher level and the colour is emitted as it falls back, the energy gap being characteristic of the element, so potassium gives lilac, sodium golden yellow, calcium brick red and barium apple green. The flame test is the simplest analytical use of atomic emission spectra. Sodium contamination easily masks the potassium colour, so it is viewed through blue glass.

19. Which property increases down group II from beryllium to barium?

• A. First ionisation energy
• B. Electronegativity
• C. Solubility of the hydroxides in water
• D. Melting point of the metal

Explanation: Hydroxide solubility rises down the group, so magnesium hydroxide is only sparingly soluble while barium hydroxide dissolves appreciably, whereas the sulphates show the opposite trend and become less soluble. Ionisation energy and electronegativity both fall down a group as the atoms get larger. This contrast between hydroxides and sulphates is a favourite examination point.

20. Carbon differs markedly from the other members of group IV mainly because it

• A. is small, has no available d orbitals and forms strong multiple bonds with itself
• B. has a much larger atomic radius
• C. is a metal
• D. has a full outer shell

Explanation: Its small size lets carbon form stable double and triple bonds and catenate into long chains, which is the basis of the whole of organic chemistry, while the absence of d orbitals limits it to a maximum covalency of four. Silicon and the heavier members can expand their octets using d orbitals, so silicon forms SiF6 2- while carbon cannot form the analogous ion. Carbon has four outer electrons, not a full shell.