The answer is: B
Explanation
The correct option is B: Extortion.
This is because A obtains property from Z by saying, "Your child is in the hands of my gang and will be put to death unless you send us Rs. 10,000/-." This amounts to intentionally putting Z in fear of any injury to Z's child and thereby dishonestly inducing Z to deliver the property to A. According to Section 383 of the Indian Penal Code, 1860, this is the definition and offence of extortion.
The other options are incorrect because they do not match with the legal definition and effect of the offence. Option A is wrong because robbery involves the direct taking of property from the victim by force or threat of force, whereas extortion involves obtaining property indirectly by coercion or intimidation. Option C is wrong because dacoity involves robbery committed by five or more persons conjointly, whereas extortion does not require any number of persons. Option D is wrong because it does not offer any alternative answer.