Solution:

You can never solve a problem on the level on which it was created.

Here is the answer key:
A-Z
B-Y
C-X
D-W
E-V
F-U
G-T
H-S
I-R
J-Q
K-P
L-O
M-N
N-M
O-L
P-K
Q-J
R-I
S-H
T-G
U-F
V-E
W-D
X-C
Y-B
Z-A

Solution:

Charcoal

Solution:

the letter 'e', which is the most common letter in the English language, does not appear once in the long paragraph :-)

Solution:

The watchman had been sleeping on the job. Otherwise, he would not have been dreaming.

Solution:

I am a Postbox

Remove as many letters as possible, still postbox remains the same.

Solution:

N for Nine

Solution:

Because the man is still living

Solution:

They are numbers for houses and it's Rs.100 per digit.

Solution:

JUPITER

Solution:

1

(Only Me)