Options turnover on India's National Stock Exchange fell to the lowest in a year on monthly expiry day, reflecting the impact of stricter trading rules and the introduction of the closing-auction system. Premium turnover declined to about 670 billion rupees ($7 billion) on Tuesday, the lowest since the bourse shifted its derivatives expiry from Thursday to Tuesday. Volumes in cash equities trading also fell to the lowest since November, highlighting a shift in market activity ahead of the exchange's initial public offering.