1. what element has 81 protons in the nuclei of its atoms?
a. platinum
b. lead
c. thallium
d. uranium

The carbon cycle is best defined as a process in which a. carbon changes from inorganic forms to organic forms and back b. carbon is changed into other elements such as oxygen or nitrogen c. carbon is continually created from the sun’s energy by plants d. carbon is consumed and regenerated from other elements such as oxygen and nitrogen