Unit 1: Should we tax sugary drinks?

An interesting clip from the BBC

http://www.bbc.co.uk/news/health-21241944#

and Aljazeera

http://www.youtube.com/watch?v=I9amsrhrUaw

a) How does the market for sugar based drinks fail?
b) Using a S&D diagram, explain how the tax would help correct the market failure
c) Comment on the likely success of such a tax policy to reduce the market failure