The answer is: " NaCl + H₂O " ; (or; write as: " H₂O + NaCl " ) .
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Specifically:
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HCl + NaOH —> NaCl + H₂O ; or; write as:
NaOH + HCl —> H₂O + NaCl .
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This type of "double-replacement" reaction is called "neutralization".
Since we are adding a strong acid to a strong base (reactants), we know that the product will be: 1) a salt ; and 2) water. Since we know one of the reactants will be "water" (H₂O) ; we can find the base (i.e. , the "remaining product") from selecting the "unused elements" to form the corresponding "salt".
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In the given situation, the gas is heated under constant volume. As energy is supplied to the system in the form of heat, the frequency of collision between the gas particles increases. This increases the temperature of the gas consequently bringing about a decrease in pressure.
Based on the ideal gas law:
PV = nRT
Here, P/T = nR/V
If P1, T1 and P2, T2 are the pressure and temperature values before and after heating respectively, then since nR/V is a constant in this case, we have
P1/T1 = P2/T2 which is the Gay-Lussac's law.
Oxidation numbers is the right answer