When you convert to you remove the placeholder zeros

Iknow the answer is a but i don't know why

After watching the video "zinc strip in copper nitrate solution", and reading the instructions, click on the link labeled "start" just below the drawing of the pencil tip. follow the direction to complete the 3x3 grid. answer the below questions for the portion of the activity in which sn(s) is placed in agno3(aq)

The fact that the total amount of energy in a system remains constant is a(n)