Anyone can help with this plzz??

Give one example to show that when substances are mixed,it may result in a chemical or a physical change depending on the conditions.

Wavelength of 125 meters is moving at a speed of 10 m/s. what is it's frequency?

What would be the radius of the earth if it had its actual mass but had the density of nuclei? express your answer to two significant figures and include the appropriate units.