Which one has the highest percentage of ionic character i)HF ii)HI iii)HCL iv)HBr

Answer option (i) Fluorine is most electronegative among them thus will pull electron cloud toward itself making the bond less covalent or more ionic.

What is the physical significance of differentiation?

Differentiation is the rate at which something is changing is changing with respect to other. For example Your velocity is the rate at which you are moving with respect to time.

Solve xdy+dy=x ? Given when y=0 x=2

The above equation can be written as, dxy=x (Use product rule dy/dx(xy)=xdy+dy Integrating both sides we get, xy=x^2/2+c y=x/2+c/x . Using the initial value 0=2/2+c/2 =>c=-4 hence, y=x/2-4/x