The wavelength of the radio photon is 268 m.
Electromagnetic waves travel with the speed of 3×10⁸m/s in vacuum. The speed of a wave <em>c i</em>s related to its frequency<em> f</em> and wavelengthλ as follows:

Thus the wavelength is given by,

Substitute 3×10⁸m/s for <em>c</em> and 1120×10³Hz for <em>f</em>.

Thus the wavelength of the radio photon from an AM station is 268 m
External force.
Air resistance, friction, grass rubbing on a rolling ball, etc.
If there is no external force on a moving object, it keeps going.
Forever !
An isotope is an atom with a different number of neutrons than another atom of the same element. Since atoms of the same element all have the same number of protons, choice B(6pro &6neu vs. 6pro&7neu) is an example of isotopes