What is the trend of ionisation enthalpies of actinoids?

What are the inner transition elements? Decide which of the following atomic numbers at the atomic numbers of the inner transition elements: 29, 59, 74, 95, 102, 104?

A green chromium compound (A) on fusion with alkali gives a yellow compound (B) which on acidification gives an orange coloured compound (C). ‘C’ on treatment with NH₄Cl gives an orange coloured product (D), which on heating decomposes to give back (A). Identify A, B, C and D. Write equations for reactions.