Step 1: Understanding the Question:
Satyashodhak Samaj (Society of Truth Seekers) was a social reform organisation formed to fight caste based discrimination and Brahmin dominance in 19th century Maharashtra.
Step 2: Recall the founding year and founder.
Jyotiba Phule founded the Satyashodhak Samaj in 1873 to work for the rights of lower castes, women, and farmers, and to oppose the idea that only Brahmin priests could interpret religious texts.
Step 3: Why the other options are wrong.
1857 is the year of the Revolt against British rule, not a reform organisation. 1875 is the year the Arya Samaj was founded by Swami Dayanand Saraswati, a different reform movement. 1829 is the year Sati was abolished under Raja Ram Mohan Roy's influence, again unrelated to this Samaj.
Final Answer:
Satyashodhak Samaj was established in 1873. This is option (C).