Virtuous means righteous and wicked means mischievous.
The Antonym of Virtuous is wicked.

Incredulous means "skeptical" or "unbelieving." It refers to a person's response. The noun form of incredulous is incredulity. The opposite is credulous, or "gullible, believes anything."

Violent: using or involving physical force intended to hurt, damage, or kill someone or something.
Tame: (of an animal) not dangerous or frightened of people; domesticated.
Humble: having or showing a modest or low estimate of one's importance.
Gentle: having or showing a mild, kind, or tender temperament or character.
Harmless: not able or likely to cause harm.

Antonym of Violent is Gentle.

Haphazard means accidental.
Deliberate means by purpose, intentionally.
So, Deliberate is opposite in meaning from haphazard.

Hollow means empty from inside or unfilled while Solid means a body covered from all sides.

Mountain means An elevation of land higher than a hill.
Valley means An area of lowland between hills or mountains.

So, we can say that Mountain is an antonym for the valley.

We would be identifying the word that is an antonym to the given word "Adherent" from the given options.
Adherent means sticking fast to an object or surface. The opposite would thus mean to draw away or divert i.e. detractor. 
If we look into the other words,
Rival means a person or thing competing with another for the same objective or for superiority in the same field of activity
Alien means belonging to a foreign country
Enemy means a person who is actively opposed or hostile to someone or something
Option B is correct 

Generous is correct as the word niggardly means ungenerous with money, time, etc.; mean while the word generous  means showing a readiness to give more of something, especially money, than is strictly necessary or expected.. Both the words are opposite in meaning.

The antonym of SUPPRESS is Encourage.