The correct order of the spin-only magnetic moments of the following complexes is :
(I) [Cr(H₂O)₆]Br₂
(II) Na₄[Fe(CN)₆]
(III) Na₃[Fe(C₂O₄)₃] ($$\Delta $$₀ $$>$$ P)
(IV) (Et₄N)₂[CoCl₄]

If 10 different balls are to be placed in 4 distinct boxes at random, then the probability that two of these boxes contain exactly 2 and 3 balls is :

The number of terms common to the two A.P.'s 3, 7, 11, ....., 407 and 2, 9, 16, ....., 709 is ______.

In the expansion of $${\left( {{x \over {\cos \theta }} + {1 \over {x\sin \theta }}} \right)^{16}}$$, if $${\ell _1}$$ is the least value of the term independent of x when $${\pi \over 8} \le \theta \le {\pi \over 4}$$ and $${\ell _2}$$ is the least value of the term independent of x when $${\pi \over {16}} \le \theta \le {\pi \over 8}$$, then the ratio $${\ell _2}$$ : $${\ell _1}$$ is equal to :