Check statement (a): Mode can be computed from histogram

Yes. For grouped data, the mode is obtained from the modal class, which is identified from the histogram as the class with the highest rectangle. Using the graphical/standard grouped-data formula, mode can be computed.

Hence, (a) is correct.

Check statement (b): Median is not independent of change of scale

If a variable $x$ is transformed to $y=\frac{x-a}{h}$ then the median also transforms accordingly: $\text{Median}(y)=\frac{\text{Median}(x)-a}{h}.$

So median changes when scale changes. Therefore, median is not independent of change of scale.

Hence, (b) is correct.

Check statement (c): Variance is independent of change of origin and scale

For the transformation $y=\frac{x-a}{h},$ variance changes as $\operatorname{Var}(y)=\frac{1}{h^2}\operatorname{Var}(x).$

Thus variance is independent of origin but not independent of scale.

Hence, (c) is false.

Conclusion

Correct statements are (a) and (b) only.

Therefore, the correct option is: $\boxed{\text{C}}$