One Word Substitution

Option (3) is correct. Antidote cures or counteracts effect of poison / or ill effects of another medicine.

Option (2) is correct.

Option (3) is correct. Avaricious means characterized by avarice; greedy; covetous. 

Option (3) is correct.

Option (4) is correct.

Correct answer is option 1.

Correct answer is option 4. Peer means equal and friends and mates are companions.

Fastidious means very attentive to and concerned about accuracy and detail, which manifests as being difficult to please or satisfy. The word comes from Latin 'fastidium' meaning loathing or disgust. Affable means friendly and approachable, obstinate means stubborn, and audacious means bold or daring.

Contemporary means living or happening in the same period of time.  

Convalescent is used to refer to a person who is recovering after an illness or medical treatment.

Fatal literally means causing death or capable of causing death. The word derives from Latin 'fatum' (fate). Dead is a state of being no longer alive, critical means seriously ill or dangerous, and alarming means causing concern or fear - but only fatal specifically means deadly.

Option 2 means a cosmopolitan person; citizen of the world.  

Germicide refers to a substance or preparation that kills germs or microorganisms. The suffix '-cide' means killing, as in homicide (killing a person) or pesticide (killing pests). Fratricide means killing one's brother, infanticide means killing infants, and pesticide kills pests generally, not specifically germs.

Immigrate specifically means to come to live permanently in a foreign country. The prefix 'im-' means 'into' and 'migrate' means to move from one place to another. Migrate is the general term for moving, hibernate means to remain inactive, and nationalize means to transfer ownership to the government.

Imperceptible means something so subtle or slight that it cannot be noticed or perceived by the senses or mind. The prefix 'im-' means 'not' and 'perceptible' means capable of being perceived. Improbable means unlikely, impregnable means unbreachable (usually fortifications), and intangible means abstract or unable to be touched.