help need some ideas?

Question

my nephew is in seventh grade and has to do a big science project. it cant be anything like a volcano. it has to have a question and experiment to prove the answer. example. which dissenfectant works best

Answer 1

There are many, many web sites which list possible science fair topics, a few of which are:
http://scienceclub.org/scifair.html
http://www.stemnet.nf.ca/sciencefairs/intermed.html
http://k12pages.r8esc.k12.in.us/allen/swacs/sciencefair/ideas.html

Your nephew should do a project which he enjoys and interests him, but also one which allows him to follow the scientific method during the experiment. Keep this in mind when choosing a topic.

A word of advice,
avoid using words like "best" and "better" when formulating a problem for a science project since these terms are subjective the observer. Instead, define exactly what you mean by "best" in the problem, then just use that word instead.

In the example you gave,
"which disinfectant works best"
by "best", I assume you meant, 'kills the highest percentage of germs', so this is what you should say instead, not leave it open to interpretation.