The benchmark Sensex at the Bombay Stock Exchange declined 52 points to 17,121.67 in the afternoon deals after gaining some momentum in the previous session. Earlier the Sensex had declined by 118 points in early trade on sustained selling by funds and retailers, amid a weak trend on Asian bourses.On the similar lines, the broad-based National Stock Exchange index Nifty stood 15.35 points at 5,207.05 in the negative territory in afternoon deals.