In order to use pythagorean theoremto find the magnitude of a resultant vector which must be true regarding the two initial vectors

The true option is a) they form a 90 degree angle.

Pythagorean theorem is valid for right triangles, which is what you can form when the two vectors have a 90 degree angle.

Regarding the other options:

b) They are equal in magnitude: this is not a condition because Pythagoream theorem is valid for any magnitude as long as the angle is 90°C.

c) They have the sam directions: false, because if the two vectors have the same directions the magnitud is the sum of the two magnitudes.

d) They are parallel: false for a similar reason that c) taking into account if they have the same direction or are opposed.  .  

If football was tossed in air without gravity or friction the ball would go into space

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.