Free Transition Elements MCQs with Answers

11. The highest oxidation state shown by manganese is

• A. plus 2
• B. plus 4
• C. plus 7
• D. plus 6

Explanation: Manganese has five 3d and two 4s electrons, so all seven can be involved in bonding, giving the plus 7 state found in the permanganate ion. That maximum equals the group number, and because the metal is so far from its stable configuration permanganate is a powerful oxidising agent. Plus 4 occurs in manganese dioxide and plus 2 in manganese two salts, which are the most stable.

12. The electronic configuration of the Fe2+ ion, given that iron has atomic number 26, is

• A. [Ar] 3d4 4s2
• B. [Ar] 3d6
• C. [Ar] 3d5 4s1
• D. [Ar] 3d8

Explanation: Neutral iron is [Ar] 3d6 4s2, and forming the two plus ion removes both 4s electrons because 4s lies above 3d once the d subshell is occupied, leaving 3d6. Removing d electrons instead and writing 3d4 4s2 is the classic mistake. Losing one further 3d electron gives the more stable half filled 3d5 arrangement of Fe3+.

13. Transition metals have higher melting points and densities than group I metals because

• A. their atoms are much larger
• B. they contain no free electrons
• C. both the d and s electrons take part in metallic bonding, giving a stronger and more compact lattice
• D. they are non metallic in character

Explanation: A larger number of delocalised electrons per atom means stronger attraction between the cations and the electron sea, so more energy is needed to melt the metal and the atoms pack more closely, raising density. Group I metals contribute only one electron each and are correspondingly soft and low melting. This is why tungsten is used for lamp filaments and sodium can be cut with a knife.

14. Zinc is not regarded as a true transition element because

• A. it is not a metal
• B. it forms no compounds
• C. it has no d electrons at all
• D. its atom and its only ion both have a completely filled 3d subshell

Explanation: Zinc is 3d10 4s2 as the atom and 3d10 as the Zn2+ ion, so it never has a partly filled d subshell and consequently shows only one oxidation state, forms colourless compounds and is a poor catalyst. It sits in the d block by position but fails the chemical test. Scandium is excluded at the other end of the row, since its only common ion, Sc3+, is 3d0.

15. Acidified potassium permanganate acts as a strong oxidising agent and in doing so the purple manganate seven ion is reduced to

• A. the almost colourless manganese two ion
• B. manganese metal
• C. the green manganate six ion
• D. brown manganese dioxide

Explanation: In acidic solution permanganate is reduced from plus 7 to plus 2, and the sharp change from deep purple to almost colourless is what makes it self indicating in titrations. In neutral or alkaline conditions the reduction stops at manganese dioxide, giving a brown precipitate instead. The acid used must be dilute sulphuric acid, since hydrochloric acid would itself be oxidised to chlorine.

16. The magnetic behaviour of many transition metal compounds is explained by the presence of

• A. paired electrons only
• B. unpaired electrons in the d orbitals
• C. an even number of protons
• D. delocalised pi bonds

Explanation: Unpaired electrons give the ion a magnetic moment, so the substance is drawn into a magnetic field and is described as paramagnetic, and the more unpaired electrons the stronger the effect. Ions with all electrons paired, such as Zn2+, are diamagnetic and are weakly repelled instead. Measuring the magnetic moment is therefore a way of counting unpaired electrons and deducing the structure of a complex.

17. An alloy such as stainless steel forms readily between transition metals because

• A. the metals react chemically to form a compound
• B. their atoms are of similar size and can substitute for one another in the lattice
• C. they have identical melting points
• D. they are all radioactive

Explanation: Atomic radii across a transition series change very little, since the added electrons enter an inner d subshell and shield the extra nuclear charge, so one metal can replace another in the lattice without disrupting it. The resulting alloy is a mixture rather than a compound. Chromium and nickel added to iron in this way give stainless steel its corrosion resistance.

18. Across the first transition series from scandium to zinc, the atomic radius

• A. increases sharply
• B. decreases sharply
• C. changes very little, because the added d electrons shield the increased nuclear charge well
• D. first increases then decreases sharply

Explanation: Each element adds a proton and a d electron, and because that electron enters an inner subshell it shields the outer 4s electrons effectively, so the net attraction on them barely changes. This near constancy is what makes transition metals so readily interchangeable in alloys. The contrast with the sharp contraction across a p block period is the point of the question.

19. Haemoglobin is a naturally occurring complex in which the central metal ion is

• A. magnesium
• B. iron
• C. cobalt
• D. copper

Explanation: Each haem group holds an iron two ion coordinated to four nitrogen atoms of the porphyrin ring, with the remaining site available to bind oxygen reversibly. Magnesium is the central ion of chlorophyll and cobalt that of vitamin B12, both of which are offered here as the parallel biological cases. Carbon monoxide is toxic because it binds the same iron site far more strongly than oxygen.

20. Vanadium pentoxide, V2O5, is used industrially as a catalyst in the

• A. Haber process
• B. hydrogenation of vegetable oils
• C. Contact process for making sulphuric acid
• D. cracking of long chain alkanes

Explanation: Vanadium pentoxide catalyses the oxidation of sulphur dioxide to sulphur trioxide, working by being reduced and then reoxidised in a cycle, which is a classic use of variable oxidation state. Iron is the catalyst for the Haber process and nickel for hydrogenation. Cracking uses zeolites, which are aluminosilicates rather than transition metal oxides.