Answer:
Krypton does not react with anything, but it reacts with fluorine gas
Explanation:
Remark
The balance numbers in front of Ag and AgNO3 are both 2. That number is in moles.
Rule: if the moles are the same in the equation, then whatever you are given for one, will be the same for the other. So you have 0.854 moles of Ag. You will also have 0.854 moles of AgNO3
Answer: 0.854 <<<<<

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.

It would contain 0.105M moles of NaOH in each liter of solution
Answer: The unknown solution had the lower concentration
Explanation: concentration will always move from higher to lower region. If the concentration of the unknown solution has increased, it therefore means that the initial concentration of the unknown solution was low