Given data:
The first expression is y=25x.
The second expression is y=5/2 x.
The third expression is y=1/4 x.
The fourth expression is y=1/25 x.
The second expression can be written as,
y=2.5x
The third expression can be written as,
y=0.25x
so, in the above expression y is proportional to x, and constant of proportionality is 0.25.
Thus, C) option is correct.