Using the student's measurements, What is the best determination that can be made about the objects? The formula for density is D = M/V.
O The objects are different substances because their masses are different.
O The objects are different substances because their densities are different.
O The objects are different substances because their volumes are different.
0 The objects are the same substance because they have the same density

An atom's smaller negative particles are at a distance from the central positive particles, so the negative particles are easier to move. 

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current

Newton's first law describes something special that results from the sum of all the external forces (including gravity) on an object.