One should not leave any topic on chance. I remember when before islamiat paper in css 2014, we were sitting outside in the garden, in govt. piolt secondary school sialkot. Most of the candidates were engaged in discussion about usury and the like. Fortunately, a thought struck me and I prepared the last 10 Surahs of the Holy Quran. Now those who have given the paper know that about 4 or 5 Mcq's were from that portion.
Alhamdulillah.