How can you identify stocks with valuation lower than that of Nifty 50?

The market sentiment has deteriorated due to the worsening situation of Israel-Hamas war, due to which Nifty has slipped by about 200 points from October 17 to 19. After this fall, are there buying opportunities in the market? If yes, then which are the companies which have lower PE valuations as compared to Nifty and can a portfolio be prepared by buying these stocks?