(a) when a chromite ore (A) is fused with an aqueous solution of sodium carbonate in free excess of air , a yellow solution of com[ound (B) is obtained . This solution is filtered and acidified with sulphuric acid to form compound (C ) . Compound (C ) on treatment with solution of KCl gives orenge crystals of compound (D ) . Write the chemical and actinoids :
(i) Greater range of oxidation states of actiniod as compared to lanthonoids .
(ii) Greater actinoid contraction as compared to lanthanoid contraction .
Lower ionisation enthalphy of early actinoids as compared to the early lanthanoids.

Explanation

(a) chemical formula of comounds A to D are given as inder :
` A=FeCr_(2)O_(4)` `B=Na_(2)CrO_(4)` `C= Na_(2)Cr_(2)O_(7)` `D=K_(2)Cr_(2)O_(7)`
(b) (i) Greater range of oxidation states actioniods than lanthanoids is because 5f, 6d and 7s levels in actinoids are of comparable enerrgies .
(ii)This is due to poorer shielding by 5f electrons in actinoids as compared to shielding by 4f electronss inlanthanoids .
(iii) In actinoids , 5f electrons are more effectiely shielded from the nuclear charge than the 4g electrons of the correspomding lanthanoids , Since the outer electrons are less firmly held , they are available for bonding in the actinoids .