The correct answer is option 1: Ahimsa (Non-violence). Gandhi believed in the power of non-violence as a means to realizing truth. Ahimsa is a principle of non-violence and compassion towards all living things. Gandhi believed that violence only breeds more violence and does not lead to long-term peace and understanding. By practicing Ahimsa, Gandhi aimed to promote harmony, justice, and reconciliation. He saw non-violence as a powerful tool for social and political change.

Option 2: Dharma (Religion) is not the correct answer. Although Gandhi was a deeply religious person, he did not believe that religion alone could lead to the realization of truth.

Option 3: Karma (Service) is not the correct answer. While Gandhi was a strong advocate for selfless service to others, it is not the primary means by which he sought to realize truth.

Option 4: Dhyana (Meditation) is not the correct answer. Although Gandhi valued meditation as a means of introspection and self-reflection, it was not the core principle he relied on to attain truth.