Science help on just 3 questions. :) 10 points for the best answer.?

[gerard]

i need a bit of help in these problems. could u tell the answers? and please double check so that i know that it really IS the right answer. thank u ;)
1. Mendeleyev sorted elements on the periodic table by grouping elements with ___________.
a. the same mass
b. similar size
c. similar properties
d. the same color

2. Every element has its own atomic number. The atomic number is the number of what in the nucleus of an atom of the element?
a. electrons
b. neutrons
c. positrons
d. protons

3. A what is the name given to a row of elements in the periodic table with densities and melting points that change gradually and predictably?