Explain the folloiwng facts: Among lanthanoids Ln(III)compound are predominant, However, occasionally in solutions or in solid compounds, +2 and +4 ions are also obtained.

An organic compound 'A' having molecular formula C_6H_6O gives a characteristic colour with aqeuous FeCI_3 solution. When 'A' is treated with CO_2 and NaOH at 400K under pressure 'B' is obtained. The compound B on acidification gives compound C which react with acetyl chloride to form D which is a popular pain killer. Deduce the structure of A, B, C and D.

Flourine is more electronegative than oxygen. Oxygen foms compound Mn_2O_7 with menganese where Oxidation state of Mn is +7 but with fluorine, menganese forms MnF_4 where oxidation state of Mn is +4 Explain.

0.05 g of an organic compound was treated according to Kjeldahl's method. The ammonia evolved was absorbed in 50 ml of 0.5 MH_2SO_4 . The residual acid required 60ml of 0.5 M solution of NaOH for neutralization. Find the percentage composition of nitrogen in the given compound.