The correct option is B Non-sister chromatids of homologous chromosome at pachytene stage of prophase-I
Prophase I of meiosis I is divided into - leptotene, zygotene, pachytene, diplotene and diakinesis.
Crossing over is the exchange of genetic materials between non-sister chromatids of homologous chromosome. It takes place at pachytene stage of prophase-I.