4. Express the answers to the following problems in scientific notation. Hint: Use the subtraction example to solve the addition problem. A. (1.8 X 1020) X (2.5 X 10^16) C. (9.2 X 10^19) ÷ (3.0 X 10^7) B.(7.9 X 10^9) - (6.0 X 10^8) D. (4.2 X 10^9) + (8.0 X 10^18)

see below

Explanation:

A. (1.8 X 10^20) X (2.5 X 10^16)

= 4.5 x 10³⁶

B.(7.9 X 10^9) - (6.0 X 10^8)

= 7.3 x 10⁹

C. (9.2 X 10^19) ÷ (3.0 X 10^7)

= 3.067 x 10¹²

D. (4.2 X 10^9) + (8.0 X 10^18)

= 8.00000002042 x 10¹⁸

  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-

i think the answer is terrae but not 100 percent sure. ▓▬▬ §