<span>Cations mix with anions, so you know NH4+ won't mix with K+ and SO4(2-) won't miix with F-. For the reason that NH4+ and F- together have single charges, they'll mix in a 1:1 ratio, NH4F. There's two charges on SO4(2-), so it'll need two K+ to mix with, K2SO4.</span>
Here you are looking on the Free Body diagram of a net force of 0N in both the x and y-directions. the only ones that has that condition met is A and C.

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.

Heavy rainfall because that’s a natural thing that happens and can never stop
Quantum Mechanical model (as per my knowledge)