Answer:
1. CYNARG
Explanation:
This a example of Caesar's Cipher, in which each letter in the original word leads to a ciphered letter according to the following equation:

In which C is the index of the Ciphered letter in the alphabet, P is the index of the original letter and o is the offset.
Finding the offset:
O is coded B
O is the 15th letter in the alphabet, so
.
B is the 2nd letter in the alphabet, so





So

PLANET:
P
P is the 16th letter in the alphabet.

So P is coded C.
L
L is the 12th letter in the alphabet:

L is coded Y(25th letter in the alphabet)
A
A is the 1st letter in the alphabet

A is coded N
N
N is the 14th letter in the alphabet

N is coded A
E
E is the 5th letter in the alphabet

E is coded R
So the correct answer is:
1. CYNARG