Why, i am sometime hesitating with my seniors, although i know very well the answers & solutions of each problem which are related to my job?

You need self-confidence bro, to have it there are2 things

1- remember this, you're manager he did before many mistakes and he learned from them that’s why he is manager and your mistakes means your developments and experience because if it’s wrong then you know how not to do it

2- Build a small case study to analyze the problem and have more than one solution to choose the best solution. This technique will help you to see the full picture and opens your mind for new strategies and solutions. Because if you understand the problem then you solved50% of the problem and to have the right tools and know how to use them then you can see the best solution. With this method you can be prepaid for the questions that you fear and you will be more realistic and logic every time you do it.

Trust yourself. There is no harm in trying. As they say, practice makes perfect. By the way, a corporate organization is a venue of everyone's opinion, knowledge and skills, meaning it is for everyone to share with, who knows your idea is the one the management is looking for. 

You lack self-confidence and this is not good. Tried to promote trust in yourself and when you are confident of your idea, encourage and try saying to your boss, even in private if you are afraid to do so in the meetings.