Solution:

276

Explanation:
6 = 1^1 + 2^1 + 3^1
14 = 1^2 + 2^2 + 3^2
36 = 1^3 + 2^3 + 3^3
98 = 1^4 + 2^4 + 3^4

Thus the next number will be
1^5 + 2^5 + 3^5 = 276

Solution:

See the figure for the answer. Wasn't it a bit tricky?

Solution:

31

Explanation:
Ramanujan lighting the candles in binary.
11110 =30
11111 =31

Solution:

Upon reaching each room, he found out that the window facing the dead body was closed. He had to open the window himself. This tells that there was somebody else with him who closed the window. If he would have committed suicide, at least one window would have been open.

Solution:

2003.

Explanation:
Its a series of prime numbes.

Solution:

'five'

Its the count of alphabet

Solution:

The woman told him to take out one nut each from the rest of the wheels and use them.

Solution:

16

Explanation:
9 [1x1] squares
5 [2x2] squares
1 [4x4] square
1 [4x4] square

9 + 5 + 1 + 1 = 16 squares.

Solution:

Yes, some people are going get really tiny pieces but you were allowed for that right. Also, there is another way of doing it. Can you think of it?

Solution:

192

Explanation:
I started with the number 192.
Adding the reversed 291 to 192 gave me 483.
Similarly,
483 + 384 = 867
867 + 768 = 1635
1635 + 5361 = 6996

Solution:

It has been clearly mentioned that all the boxes are labeled incorrectly. If he opens the Box3, then he will get either Dark Chocolates or Milk Chocolates as it is labeled incorrectly. Let us suppose he finds Dark Chocolates in there. Now since all are labeled incorrectly, Box B A must contain Milk Chocolates and Box B must contain Milk Chocolates and Dark Chocolates.