The correct answer is option 4: Sodium chloride. Sodium chloride, commonly known as table salt, is an important chemical in our struggle for freedom. It has played a significant role in various historical events and movements.

During the time of the British Raj in India, the British imposed a tax on salt, known as the Salt Act. This act prohibited Indians from producing or selling salt, forcing them to buy it from the British at high prices. This led to widespread protests and civil disobedience movements, with Mahatma Gandhi leading the famous Salt March in 1930. The Salt March was a nonviolent protest against the British monopoly on salt production, symbolizing the fight for freedom and independence.

Salt became a powerful symbol of resistance and a catalyst for the Indian independence movement. It represented the struggle against unfair colonial policies and the fight for self-reliance. The choice of sodium chloride as a symbol was significant because it was a common and essential chemical used in everyday life.

Therefore, sodium chloride was an important chemical symbol in our struggle for freedom.