I do not know why the Binance adds a new trading pairs for a ripple, but this will obviously lead to an increase of the price of XRP. I do not believe in the ripple itself but you can buy it just to take some profit
ripple trading pairs on binance will increase the trading volume of ripple,,
but not the price,, because price will increase if a demands coming,, somebody could correct me if i'm wrong

Yes and no, I guess. Having Ripple as a base trading pair can also mean that people will buy XRP to trade on Binance, especially if they want to hold on to BTC and ETH, which a lot of people will want to do now. At the same time, XRP volume trading means there's more XRP earnings for Binance in terms of commission. More available XRP to sell and at more competitive rates = more demand? Hard to tell with Ripple!