What do we call atoms of the same elements with different mass numbers?

Achemistry student weighs out 0.306 g of citric acid (h3c6h5o7), a triprotic acid, into a 250 ml volumetric flask and dilutes to the mark with distilled water. he plans to titrate the acid with 0.1000 m naoh solution. calculate the volume of naoh solution the student will need to add to reach the final equivalence point. be sure your answer has the correct number of significant digits.

Calculate the percent composition by mass of each element in al(oh)3. use at least three significant figures.

An alpha particle is: a hydrogen atom a nucleus of helium two neutrons an electron