Which of the following numbers is correctly rounded to three significant figures, as shown in brackets?
a. 12,556 [12,500]
b. 4.5671 × 10^-9 [4.567 ×10^-9]
c. 3.00072 [3.001]
d. 0.006739 [0.00674]
e. 5.4589 × 10^5 [5.459 ×10^5]

D is correctly rounded to three significant figures.

Explanation:

A is incorrect because although it has 3 significant figures, it is rounded incorrectly. The correct answer would be 12,600.

B is incorrect because is rounded to 4 significant figures instead of three.

C is also incorrect because is rounded to 4 significant figures instead of three.

D is correctly rounded to three significant figures.

E is also incorrect because is rounded to 4 significant figures instead of three.

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.