Option (ख) is correct because the provided text clearly states that people started discussing the boy's sense of justice ('लोग लड़के की न्याय-बुद्धि की चर्चा करने लगे') and slowly this news reached the king's ears ('धीरे-धीरे यह बात राजा के कानों तक पहुँची'). This directly matches the option stating that the king found out by hearing the people's praise of the boy's justice.