The formula of capacitance for capacitor in case of spherical capacitors is given by

C = 4πE₀ ab/ (b-a)            where , E₀ = permittivity in air.

                                                    a,b = radii of the two scherical surfaces

From the above relation,

Capacitance is : 1) directly proportional to the product of the radii

                         2) inversely proportional to the difference between the two radii.

My doubt is that if I Increase 'b' then there is no doubt that the product increases and there is increase in the value in the numerator, but even the difference increases in the denominator and then the value can decrease. I am confused at this point. How do I tackle this situation ?

put it as

1/c=k(1/a-1/b)

if b increases 1/c increases bcoz 1/b decreases and hence c decreases

take reciprocal both sides ,,,,,

 u ll get 1/C=k(1/a-1/b)

if u increase b then 1/b decreases value of bracket increase and so C dec(a is kept cans) as 1/C inc.......................