Answer:
- <em>The mystery substance is</em> <u>C. Bromine (Br) </u>
Explanation:
<em>Argon (Ar) </em>is a noble gas. Whose freezing point is -189 °C (very low), thus it cannot be the frozen substance. Also, it is not reactive, thus is would have not reacted with iron. Hence, argon is not the mystery substance.
<em>Scandium (Sc) </em>is a metal from group 3 of the periodic table, thus is will not react with iron. Thus, scandium is not the mystery substance.
Both <em>bromine</em> and <em>iodine</em> are halogens (group 17 of the periodic table).
The freezing point of bromine is −7.2 °C, and the freezing point of iodine is 113.7 °C. Thus, both could be solids (frozen) in the lab.
The reactivity of the halogens decrease from top to bottom inside the group. Bromine is above iodine. Then bromine is more reactive than iodine.
Bromine is reactive enough to react with iron. Iodine is not reactive enough to react with iron.
You can find in the internet that bromine vapour over hot iron reacts producing iron(III) bromide. Also, that bromine vapors are red-brown.
Therefore, <em>the mystery substance is bromine (Br).</em>
The observation in the illustration remains in accordance with the law of conservation of mass assuming that moisture is present in the container.
<h3>What is the law of conservation of mass?</h3>
The law state that mass can neither be created nor destroyed. However, mass can be converted from one form to another.
In this case, the ion was placed in a container of pure oxygen. Assuming that moisture is present, iron reacts with oxygen to form rust according to the following equation:

The rust formed will weigh more than the initial weight of the iron.
Without the presence of moisture, one can effectively conclude that the observation violates the law of conservation of mass.
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They have six valence electrons
A change will only occur one time in unidirectional.
Because
Cyclic : Cyclic compounds are chemical compounds having a basic non-linear structure. In other words, these are ring structures. One or more series of atoms in the compound is connected to form a ring structure.
Periodic : The periodic table of chemical elements, often called the periodic table, organizes all discovered chemical elements in rows (called periods) and columns (called groups) according to increasing atomic number.
Unidirectional : compound is operating or moving in one direction only and it does not move in other direction.
Bidirectional : Capable of reacting or functioning in two, usually opposite, directions.
Thus, A change will only occur one time in unidirectional.
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Answer : The amount of heat released, 45.89 KJ
Solution :
Process involved in the calculation of heat released :

Now we have to calculate the amount of heat released.
where,
Q = amount of heat released = ?
m = mass of water = 27 g
= specific heat of liquid water = 4.184 J/gk
= specific heat of solid water = 2.093 J/gk
= enthalpy change for fusion = 40.7 KJ/mole = 40700 J/mole
conversion :
Now put all the given values in the above expression, we get
(1 KJ = 1000 J)
Therefore, the amount of heat released, 45.89 KJ