One ball rolls along a shelf at a steady rate. a second ball rolls off the shelf and gains speed as it falls in a curved path. which must have an unbalanced force acting on it?

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.

catya your not at all which answer i've seen you do this on another question!