The answer is b. as a whole, the species is mutually beneficial to carry on each others traits and exist in the same ecosystem.
Answer:
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As long as the equation in question can be expressed as the sum of the three equations with known enthalpy change, its
can be determined with the Hess's Law. The key is to find the appropriate coefficient for each of the given equations.
Let the three equations with
given be denoted as (1), (2), (3), and the last equation (4). Let
,
, and
be letters such that
. This relationship shall hold for all chemicals involved.
There are three unknowns; it would thus take at least three equations to find their values. Species present on both sides of the equation would cancel out. Thus, let coefficients on the reactant side be positive and those on the product side be negative, such that duplicates would cancel out arithmetically. For instance,
shall resemble the number of
left on the product side when the second equation is directly added to the third. Similarly
Thus
and

Verify this conclusion against a fourth species involved-
for instance. Nitrogen isn't present in the net equation. The sum of its coefficient shall, therefore, be zero.

Apply the Hess's Law based on the coefficients to find the enthalpy change of the last equation.

Answer:
2NaBr + I2 Right arrow. 2NaI + Br2
2AgNO3 + Ni Right arrow. Ni(NO3)2 + 2Ag
Explanation:
The activity or electrochemical series is an arrangement of elements according to their order
of reactivity.
If we look at the reactions, one thing that we must note is that the reactions that can occur are those in which an element that is higher in the series displaces another element that is lower in the series.
Br is higher in the electrochemical series than I so it can displace it. Ni is higher than Ag in the electrochemical series hence it can displace it.