The correct option is B Value of static friction is always greater than kinetic friction.
Friction is a parallel component of contact force that results due to the forces acting between the charged components (i.e electron, proton) of atoms of the two bodies/surfaces in contact.
∴ Friction is an electromagnetic force.
⇒The relation between coefficient of static and kinetic friction is μs≥μk
But value of static friction is not always greater than kinetic friction. Static friction fs adjusts its value in the range (0≤ fs≤μsN) to prevent the relative motion between surfaces in contact.
⇒ Once slipping happens then kinetic friction (fk=μkN) acts on body, which is constant.
∴ Option (b) is the incorrect option.