The incorrect statement regarding the transition metals is:

1.	They are malleable and ductile.
2.	They have high melting and boiling points.
3.	They crystallise with body-centered cubic and hexagonal close-packed structure only.
4.	They show variable oxidation states although not always.

Assertion: Transition metals have high boiling points and high enthalpy of atomization.

Reason: The transition metals occur in bcc, hcp or ccp structures charcterstics of metals.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion
3. Assertion is true but reason is false
4. Both assertion and reason are false

Assertion: Zn, Cd and Hg are normally not considered transition metals.

Reason: d-orbitals in above elements are completely filled, hence above metals do not show the general charcterstic properties of the transition elements.

Assertion :A transition metal forms alloy with other transition metal easily.

Reason: The transition metals have similar electronic configuration,nearly equal radii and exhibit similar packing in their lattices.

Assertion : Anhydrous copper(II) chloride is a covalent while anhydrous copper(II)fluoride is ionic in nature.

Reason: In halides of transition metals, the ionic character decreases with increase in atomic mass of the halogen.

Assertion: E^o for Mn³⁺/Mn²⁺ couple is more positive than for Fe³⁺/Fe²⁺.

Reason: Mn³⁺ has d⁴ configuration and Fe³⁺ has a d⁵ configuration.

Assertion: Transition metals exhibit higher enthalpies of atomization.

Reason: The atoms of transition metals are held together by strong metallic bonds.

Assertion : The transition elements form interstitial compounds.

Reason: Steel and cast iron are hard due to the formation of an interstitial compound with carbon.

When iron becomes passive by "X", it is due to the formation of "Y". X and Y, respectively, are:

1. Dil. HCl, ${\mathrm{Fe}}_2{\mathrm{O}}_3$

2. 80% Conc. ${\mathrm{HNO}}_3$, ${\mathrm{Fe}}_3{\mathrm{O}}_4$

3. Conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$, ${\mathrm{Fe}}_3{\mathrm{O}}_4$

4. Conc. HCl, ${\mathrm{Fe}}_3{\mathrm{O}}_4$

When KMnO₄ solution is added to hot oxalic acid solution, the decolorization is slow in the beginning but becomes instantaneous after some time. This is because : 

1. ${\mathrm{Mn}}^{2+}$ acts as auto catalyst.

2. ${\mathrm{CO}}_2$ is formed.

3. Reaction is exothermic.

4. ${\mathrm{MnO}}_4^{-}$ catalyses the reaction.