Could you guys help me out on this percent yield question?

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

Ithink its called the coefficent.

3-isopentane; 3-methylbutane, and 1,2-methylpropane do not meet iupac rules, so they are wrong names.the only valid name onthe list is 2-methylbutane, which is the same isopentane.this is its formula:                   ch2                    |ch3 - ch - ch2 - ch3answer: 2-methylbutane