The answer is; D
While electromagnetic waves travel at an astounding 3.00 x 10^8 m/s and any delay seems imperceptible in short distances, in long distances, the waves take some time to reach the other end. This is why there is usually a small delay when ground communication tries to reach astronauts in space. Also, remember that when a communication is relayed from the earth, it has to reach the destination and then wait for a response back to earth which covers the same distance or longer/shorter if the target is moving.
The distance to the moon is 384,400 km, therefore multiply this by 2 = 768,800 km
768,800,000m/300,000,000m = 2. 56 seconds
Therefore radio waves sent to the moon from earth will have a minimum 2.5 seconds delay not considering the processing time of this communication by the destination before sending feedback. ‘Over to you’ signals end of a message by the messenger hence allowing the other messenger on the other to respond.
<u>Answer:</u> The correct option is 1 mole of acetic acid was required for 2 moles of sodium bicarbonate
<u>Explanation:</u>
We are given:
Average number of drops of sodium bicarbonate = 142
The chemical equation for the reaction of sodium bicarbonate and acetic acid in vinegar follows:
From the stoichiometry of the reaction:
1 mole of sodium carbonate reacts with 1 mole of acetic acid in vinegar.
Hence, the correct option is 1 mole of acetic acid was required for 2 moles of sodium bicarbonate
Pure substances can or can not be chemically combined.
Pure substances can be either elements or compounds, but not mixture. Mixture are different substances mixing together without being chemically combined, such as air, which is a mixture of oxygen, carbon dioxide, water etc. Mixture can be separated by physical methods, like filtration or decantation.
Meanwhile, elements are the substances that cannot be further separated by any means. No matter physical or chemical methods. Examples of elements are oxygen, hydrogen, neon and all the other ones from the periodic table. Compounds are basically elements joining together, but they’re chemically combined which means their electrons (kind of subatomic particle) are either shared or given away. These elements can only be separated by chemical methods like electrolysis or heating.
Therefore, as long as the substance cannot be separated by physical methods, it can be considered as a pure substance. We can now conclude that pure substance can be (element) or can not be (compound) chemically combined.
