Which of the following are isotopes? a u-235, br-81 b mg-12, mn-55 c cl-35, cl-37 d h-1, h-1

C) Cl-35 & Cl-37

Explanation:

Isotope: a form of an element that differs only in the number of neutrons in the nucleus.

A & B are wrong because U and Br are two different elements, so are Mg and Mn.

D is a trick question because H-1 is the same as H-1, therefore they can't be isotopes.

  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-