Which two statements are true?
the definitions for electric force and electromagnetic force are identical.
electric forces and magnetic forces are different aspects of a single electromagnetic force.
the operation of a motor depends on the relationship between electric and magnetic forces.
a magnet must be moving for a magnetic force field to exist.

These two statements are true:

"Electric forces" and "magnetic forces" are different aspects of a "single electromagnetic force".

The "operation of a motor" depends on the relationship between "electric force" and magnetic forces".

Option: B and C

Explanation:  

As per the definition of electromagnetic forces, Electromagnetic forces are fundamental forces that take place between electrically charged particles where it is responsible for "electrostatic force" while "magnetic force" carried between objects by "photons" and responsible for "magnetic field". Therefore "Electric force" and "magnetic force" are two important phase of "electromagnetic force". And operation of motor which converts "electrical energy" into "mechanical energy" is dependent on both of these forces.

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years

it takes on an electronical energy