Why and when was the word 'Socialist' added to the Preamble of the Constitution of India?

Give one reason why the makers of Constitution wanted India to be a Secular State.

Read the following excerpt and answer the questions that follow:

India's commitment to the rule of law is grounded in the Constitution which establishes India as a 'Sovereign Socialist Secular Democratic Republic' with a Parliamentary form of Government. The Constitution of India is the supreme legal authority which binds the legislative, executive, and judicial organs of government.

(Source: https://www.sci.gov.in/constitution/)

(a) How does India function as a sovereign state?

(b) Highlight differences between democratic and republic.

The Constitution of India is introduced to us through a Preamble. In this connection explain the following :

(a) The meaning of Preamble.

(b) Its significance.