Choose the correct alternative to complete the series: $aa...aaa.....aaaa...aaaa...b$

To answer these questions, study the following arrangement of digits, letters and symbols carefully.

$6, N,P ,=,@, 7,1 ,\&, R, T, 3, L, ,B, \star, E ,4,\# , 8, G,H ,\$, 5, K,M ,?, 2, D,C$

How many such digits are there in the arrangement each of which is immediately followed by a symbol but not immediately preceded by a letter?

Complete the series: $4, -8, 16, -32, 64, (\ldots)$

The following questions are based on the five three-digit numbers given below:
$972, 526, 487, 359, 251$
If the digits in each of the above numbers are written in reverse order,which will be the second highest number?

Choose the term which will continue the following series :
$P 3 C , R 5 F , T 8 I , V 12 L , ?$

Choose the correct alternative for the missing term.
$?, siy, oeu, kaq, gwm, cri$