Correct Answer: (a) Hindustan Zinc Ltd.
Note: Main industrial units in Rajasthan run by the Central Government are – Hindustan Zinc Limited, Udaipur; Hindustan Machine and Tools Limited, Ajmer; Hindustan Sambhar Salts Limited, Jaipur; Hindustan Copper Limited, Khetri; Modern Food Industries, Jaipur; Rajasthan Electronic and Instrument Limited, Kanakpur and Instrumentation Limited, Kota.