D. Is the best indicator for a chemical change.
The –OH+ group is most acidic proton in ln-OH as shown in figure (a). The proton is circled in the figure.
The stabilisation of the conjugate base produced is stabilises due to resonance factor. The possible resonance structures are shown in figure (b).
The acidity of a protonated molecule depends upon the stabilisation of the conjugate base produced upon deprotonation. The conjugate base of ln-OH is shown in figure (a).
The possible resonance structures are shown in figure (b). As the number of resonance structures of the conjugate base increases the stabilisation increases. Here the unstable quinoid (unstable) form get benzenoid (highly stable) form due to the resonance which make the conjugate base highly stabilise.
Thus the most acidic proton is assigned in ln-OH and the stability of the conjugate base is explained.
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Answer:
Copper sulphate is an acidic salt: It is the product of the reaction between a weak copper base and a strong acid , H2SO4
Litmus has a red colour in acidic solutions:
Conclusion: Acidic copper sulphate solution turns blue litmus to red
Baking soda is a basic salt : It is the reaction product of a weak acid , CO2 and a strong base , NaOH
Litmus has a blue colour in basic solutions:
Conclusion: basic baking soda solution turns red litmus to blue
Answer : The molar mass of hemoglobin is, 
Explanation : Given,
Molar mass of iron = 55.85 g/mol
0.349 % Fe by mass that means 0.349 grams of Fe present in 100 grams of hemoglobin.
or,

Now put all the given values in this formula, we get:


Thus, the molar mass of hemoglobin is, 