In a situation wherein A (female) and B (male) are working in same office, same designation, same nature of work but unequal payment, which of the following Articles of the Constitution will be applicable?

The correct option is Article 39(d).

Explanation:
Article 39(d) of the Constitution of India comes under the Directive Principles of State Policy (DPSP) in Part IV.
It directs the State to secure that there is equal pay for equal work for both men and women. In a situation where a female employee and a male employee are working in the same office, holding the same designation, and performing the same nature of work, paying them unequally violates the principle enshrined under Article 39(d).

Overview of other options:
• Article 21: Protects Protection of Life and Personal Liberty.
• Article 48A: Deals with the protection and improvement of the environment and safeguarding of forests and wildlife.
• Article 18: Deals with the abolition of titles.