The correct answer is (a). Protection from discrimination on grounds only of religion, race, caste, sex or place of birth.
All persons are equal before the law and are entitled to equal protection of the laws. No person shall be discriminated against on grounds only of religion, race, caste, sex or place of birth.
This right is available to any person on the soil of India, whether citizen or foreigner. It is a fundamental right and cannot be taken away by any law.
The other options are not fundamental rights.
(b) Equality of opportunity in matters of public employment is a right available only to citizens of India.
(c) Cultural and educational rights of minorities are rights available to minorities, i.e., groups of people who are different from the majority in terms of religion, language, culture or any other aspect.
(d) Right against exploitation is a right available to all persons, but it is not available to foreigners who are in India on a temporary basis.