a well accepted theory in science is that through chemical means, matter cannot be created or destroyed. because it is well - accepted , it has been proven to be true.

true
false

true

Most High school teachers would say true.

A few college teachers that understand relativistic effects would say false, all energy involved in chemical (or nuclear) reactions translates to lost mass. In fact, chemical bonding enery is in fact recorded in mass changes in the atom (very, very slight changes). Read the binding energy and mass equivalence paragraph. Dynamite is a chemical reaction.
http://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence

I would say false because a theory isn't proven just because it's well accepted.

I agree. False for both reasons stated by BobPursley and MsSue

The statement is true. The principle that matter cannot be created or destroyed is known as the law of conservation of mass. This law is a fundamental concept in chemistry and is based on extensive experiments and observations. It states that in a closed system, the total mass of the substances before and after a chemical reaction remains constant. This principle has been extensively tested and is considered to be a well-accepted theory in the field of science.