A. True
They are formed behind an obstacle when the wind blows the sand up to it.
Answer:
A. 
B. 
Explanation:
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In this case, since the undergoing chemical reaction between nitrogen and hydrogen is:

Thus we proceed as follows:
A. Here, we first need to compute the moles of ammonia yielded by each reactant, in order to identify the limiting one:

Thus, since nitrogen yields the fewest moles of ammonia, we realize it is the limiting reactant, so the theoretical yield, in grams, of ammonia is:

B. Finally, since the actual yield of ammonia is 1.23, the percent yield turns out:

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<span>La Nina a cooling of water in the Pacific that happens at irregular intervals and is associated with widespread changes in weather patterns complementary to those of El Niño, the heating of water. It is at the least less extensive and damaging in their effects.</span>