Concept:
Under the Constitution of India, the Lok Sabha enjoys greater powers than the Rajya Sabha in financial matters. Financial Bills and Money Bills originate in the Lok Sabha, and the Rajya Sabha has only limited powers regarding them.
Step 1: Recall the Constitutional provision.
Financial Bills are introduced only in the Lok Sabha on the recommendation of the President. The Lok Sabha has the final authority in financial matters.
Step 2: Analyse the options.
• Railway Budget -- Incorrect.
• Fundamental Rights -- Incorrect.
• Foreign affairs -- Incorrect.
• Financial Bill -- Correct.
Step 3: Final conclusion.
Hence, Lok Sabha has supremacy in matters relating to
\[
\boxed{\text{Financial Bill}.}
\]