Answer: 
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
Thus in the reactants, there are 2 atoms of hydrogen and 2 atoms of iodine .Thus there has to be 2 atoms of hydrogen and 2 atoms of iodine in the product as well. Thus a coefficient of 2 is placed in front of HI.
The balanced chemical reaction is:

Hey there!
The elements in this equation are K, N, O, H, and C.
Let's count how many of each are on each side to see if it is balanced.
K: 2 on the left, 2 on the right.
<em>N: 2 on the left, 4 on the right. </em>
<em>O: 9 on the left, 6 on the right. </em>
<em>H: 2 on the left, 4 on the right. </em>
C: 1 on the left, 1 on the right.
Notice that there are different amounts of N, O, and H on the left side and the right side.
This means that the equation is not balanced.
Hope this helps!
Scientists repeat experiments for reliability. Experiments have to be repeated, since performing an experiment only once, does not prove a scientists theory on the experiment, which they develop by performing the experiment. And then performing the experiment again or even many times to prove or disapprove their theories. Btw, before an experiment begins, the scientist will make a hypothesis of what they believe will happen. If proven correctly, they would then use those results they record throughout the experiment, from beginning to end to prove whether or not their hypothesis are correct or incorrect. Click to let others know, how helpful is it
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So that they can prove the other scientists views wrong and develop a new theory in which there is more sense and credibility.
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BASICALLY, I THINK THE ANSWER IS 1 OR 2 OR
To answer the question above, we take note first that every mole of PCl₃ contains 3 atoms of Cl. First, we divide the given number by 3.
3.68 x 10²⁵ / 3 = 1.227 x 10²⁵
Then, we divide the answer by the Avogadro's number which is equal to 6.022 x 10²³. That is,
1.227 x 10²⁵ / (6.022 x 10²³) = 20.37
Thus, there are 20.37 mol of PCl₃.