I have get 30marks in WB Jee what rank obtained in open categories by this marks

Hello Praveen Kumar singh. If by open category ,you mean Outside state category then with score of 30 in wbjee , ranking would be around 25k. Now with such rank it would be difficult to get a decent college under wbjee. However you can give it a try if you are willing to go till the last round.

I myself appeard for the wbjee previous year and scored 70 marks and my rank was 4350(approx).But as we go down below 45 marks a single difference in the marks creates a gap of huge rank. On the basis of previous scenario and present questions quality you can accept a rank of about 25k-30k

You can also predict your rank through the rank predictor available on internet but my experience shows that only very few are genuine and some of the predictor shows a very worst rank card so don't get panic and be selective in this.

All the best!