Question

Which of the following snakes is poisonous?
A. Cobra
B. Krait
C. Afai
D. All of above

Answer 1

Hint:
The snakes are the legless, elongated carnivorous organisms that belong to suborder Serpentes and phylum Reptilia. They may or may not produce venom. Those who produce poison are also known as venomous snakes. These secrete poison to immobilize their prey; it is sometimes also used as their defense mechanism.

Complete answer:
Venomous snakes belong to the species of suborder Serpentes that have the ability of producing venom which is used for killing their prey, for their defense, and to assist the digestion of their prey. The delivery of venom is through injection using hollow or grooved fangs, even though some venomous snakes lack well-developed fangs. Some of the venomous snakes that are found in India are:
Cobra: Cobra is the common name of various elapid snakes, belonging to the genus Naja. All of the cobras are venomous and many of them are capable of rearing upwards and produce a hood when threatened.
Krait: The common krait (Bungarus caeruleus) is also known as Indian krait or blue krait is a species of highly venomous snake of the genus Bungarus found in India. It is one of the "big four" species, out of which the most snakebites are imposed on humans in Bangladesh and India.
Afai: Afai is called Echis carinatus. It is a venomous viper species found in parts of the Middle East and Central Asia, and especially India. It is the smallest member of the big four snakes that are responsible for causing the most snakebite and deaths. Echis carinatus is native to Asia. It is found in India, Sri Lanka, Bangladesh, and Pakistan (including Urak near Quetta and Astola Island off the coast of Makran) in Indian subcontinent.

Since, all three of these are found in Indian subcontinent therefore the answer to this question is all of these i.e. last option.

Additional information:
The evolutionary history of venomous snakes can be traced back to as far as 25 million years ago. Snake venom is in fact modified saliva which is used for immobilization of its prey and self-defense. It is usually delivered through highly specialized teeth and hollow fangs directly into the bloodstream or tissue of the target organism. The venom was present in small amounts in the ancestors of all snakes as well as several lizard families as "toxic saliva" and evolved to extremes in those snake families that are normally classified as venomous by parallel evolution.

Note:
The toxicofera hypothesis implies that "nonvenomous" snake lineages have either lost the ability to produce venom or actually produce venom in small quantities which is sufficient to help capture small prey but do not cause harm to humans if bitten.