What must differ between the atom of two different element easy 10 points

Can someone me with 6 to 10 plz this is for masteries test.

1) a light bulb takes in 30 of energy per second. it transfers 3j as use energy. calculate the efficiency. second. it transfers 3j as useful light energy and 27j as heat energy. calculate the efficiency

Which of the following reasons best explains why a scientist would want to replicate gregor mendel's pea plant experiment? a. to discover new aspects of the natural world b. to test the predictions of current theories c. to explain recently observed phenomena d. to test the conclusions of prior investigations