An element's atomic number is 66. how many electrons would an atom of this element have?

The atomic number is the amount of electrons an atom has, therefore:

An atom with 66 as it's atomic number has 66 electron and 66 protons (if the atom is neutral, if not, things are different).

Hope it helped,

BioTeacher101

the overall balanced equation

6co2 + 6h2o > c6h12o6 + 6o2

sunlight energy

where: co2 = carbon dioxide

h2o = water

light energy is required

c6h12o6 = glucose

o2 = oxygen