Because of internal friction between layers of mud particles called viscosity. When you walk, your foot exerts a force on the mud; and according to Newton, the mud also (is supposed to) exert an equal opposite force, which leading to an equal net resultant force in your direction, propelling you forward.
Iodine, chloride, and bromide
The answer is; Irregular.
When crest of one wave interferes with the trough of other wave, the amplitude of the resultant wave formed is less. Hence the type of interference is destructive interference.
To solve this problem we will apply the concepts related to Coulomb's law for which the Electrostatic Force is defined as,

Here,
k = Coulomb's constant
= Charge at each object
r = Distance between them
As the distance is doubled so,





Therefore the factor is 1/4