There are certain trends with which you should become very familar (recognizing these trends will save you time!) This part of the question is dedicated to that task.

a) Whenever you see 9 or a multiple of 9 in the integration ratio, which group should you first consider for being responsible for that signal.
b) Whenever you see a quartet and triplet on a spectrum, which group should you first consider for being responsible for those signals?
c) Whenever you see septet and a doublet on a spectrum, which group should you first consider for being responsible for those signals?
d) Whenever you see 6 or a multiple of 6 in the integration ratio, which group should you first consider for being responsible for that signal
e) Whenever you see 3 as the actual number of protons for a given signal, which group should you first consider for being responsible for that signal

Explanation:

The objective of this  question is all about identifying the phenomena that holds true for the statement being said in each instance. Let; walk through them.

a) Whenever you see 9 or a multiple of 9 in the integration ratio, which group should you first consider for being responsible for that signal.

( C₄H₉ )Tert. Butyl group

b) Whenever you see a quartet and triplet on a spectrum, which group should you first consider for being responsible for those signals?

(CH₃CH₂)  ethyl group

c) Whenever you see septet and a doublet on a spectrum, which group should you first consider for being responsible for those signals?

(CH(CH₃)₂)  isoproply group

d) Whenever you see 6 or a multiple of 6 in the integration ratio, which group should you first consider for being responsible for that signal

(CH(CH₃)₂)  isoproply group

e)  Whenever you see 3 as the actual number of protons for a given signal, which group should you first consider for being responsible for that signal.

CH₃- methyl group

A perfect description showing  the explanation of each answers chosen is explained with an aid of diagram below.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.

- decrease the number of plants and animals living in the water.