What does the nucleus of the atom contain? A. protons and electrons
B. protons and neutrons
C. neutrons and electrons

An alloy contains 66 g of pure zinc. what is the percentage of zinc in the alloy? express your answer to two significant figures and include the appropriate units.

Awhite powder is added to a solution. the images show observations made before the powder is added, just after the powder has been added, and a little while later. (the liquid in the small beaker is phenol red solution.) what evidence shows that a chemical change has taken place?

Give one example of a pure (exact) number and of an estimated (measured) number.