A student has two solid blocks that have different masses. The student knows that each block is composed of a pure substance, but she wants to know if the blocks are composed of the same pure substance. Which of these would best show that the blocks are composed of different substances? A.
Both blocks can be scratched by a piece of glass.
B.
One block has a greater volume than the other block.
C.
Both blocks sink when placed in water.
D.
One block conducts electricity and the other does not.

The answer is maybe B hope it helps

the answer for sodium is 0.186

the answer for rubidium is 0.251

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-