Answer: Strong 128-bit encryption.
Explanation: An individual character corresponds to 8 bits . So if there are 16 characters then,
168=128 bits keys
This makes the 128 bit key encryption the strongest amongst all other options.It is strongest because it is almost impossible to decode the 128-character key by any method e.g.-brute-force method.
Other options are incorrect because the characters given by the other bits are as follows: =32 characters
=64 characters
=128 characters
Thus, the strongest character key is of 128 bits. for cipher.