Independent variable would be salt since you can't change it in this experiment.
Explanation:
Higher the frequency smaller will be the wavelength. Higher frequency have shorter wavelength and lower frequency waves have larger wavelength. Also, Beats are formed by the superposition of two waves with slightly different frequencies but with similar amplitudes. In time, waves switch between constructive interference and disruptive interference, giving the resultant wave a time-varying amplitude.
The answer is (2). If you recall Rutherford's gold foil experiment, remember that a stream of positively charged alpha particles were shot at a gold foil in the center of a detector ring. The important observation was that although most of the particles passed straight through the foil without being deflected, a tiny fraction of the alpha particles were deflected off the axis of the shot, and some were even deflected almost back to the point from which they were shot. The fact that some of the alpha particles were deflected indicated a positive charge (because same charges repel), and the fact that only a small fraction of the particles were deflected indicated that the positive charge was concentrated in a small area, probably residing at the center of the atom.
There are several differences between a physical and chemical change in matter or substances. A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.
