C

The equation of the stationary wave is given by
y = 2A \, sin\left(\frac{2\pi ct}{\lambda}\right) \, cos\left(\frac{2\pi x}{\lambda}\right).
Here, c is the speed of the wave, A is the amplitude, and \lambda is the wavelength.
Option A: states that the unit of c is same as that of f. This is true, as both have units of m/s.
Option B: compares the unit of A (amplitude) with p (pressure), which are not the same, hence this could be true.
Option C: compares units erroneously with \lambda (wavelength) being compared to k (wave number), which are different (meters vs reciprocal meters).
Option D: compares f (frequency) with c and \lambda appropriately, which holds true according to f = \frac{c}{\lambda}.
Therefore, the incorrect statement is C.