Which is the most important property of a stationary wave?

$A$ standing wave having $3$ nodes and $2$ antinodes is formed between two atoms having a distance of $1.21 \ Å$ between them. The wavelength of the standing wave is (in $Å$)

The wave pattern on a stretched string is shown in the figure. Interpret what kind of wave this is and find its wavelength.

$A$ sound source of frequency $170 \, Hz$ is placed near a wall. $A$ man walking from the source towards the wall finds that there is a periodic rise and fall of sound intensity. If the speed of sound in air is $340 \, m/s$,the distance (in metres) separating the two adjacent positions of minimum intensity is

$A$ wave represented by the equation $y = a \cos (kx - \omega t)$ is superposed with another wave to form a stationary wave such that the point $x = 0$ is a node. The equation for the other wave is:

At nodes in stationary waves,