<span>A) Frequency due to motion
As you are moving toward the object that is making the sound the frequency is higher. When you begin to move away the frequency lowers.
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Water levels tend to drop in dry weather because of evaporation. The hot temperatures will cause the water to achieve its gaseous state and go up into the atmosphere.
Helium has more protons making it heavier by one atomic mass.
False. Pb is lower than Al in the reactivity series. It cannot replace aluminium in AlCl3
