Answer:
Exothermic reaction for the HCl, endothermic reaction for the water

Explanation:
Heat was lost by HCl as its temperature lowered, so it was an exothermic reaction for the HCL.
Heat was gained by water as its temperature increased, so it was an endothermic reaction for the water.
m = Mass of water = 100 g
c = Specific heat of water = 
= Change in temperature of water = 
Heat is given by

Heat gained by water is
.
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Equate the gravitational force to the electrostatic force:
<span>KC²/D² = Gm²/D² → C = m√[G/K] = 7.6√[6.67E-11/9E9] = 6.54E-10 coulombs </span>
<span>Number of electrons N = 6.24E18*C = 4.083E9 electrons</span>
<span>Hydroxy group..
... :):) ....</span>
The correct answer is C) A substance changes color when heated, but changes back when cooled. Hope this helps.