Correct Answer  Option 4 : parabolic function
Concept:
The deviation of the output of the control system from the desired response during steadystate is known as steadystate error.
Steadystate error, \({e_{ss}} = \mathop {\lim }\limits_{s \to 0} \frac{{sR\left( s \right)}}{{1 + G\left( s \right)}}\)
Input

Type0

Type1

Type2

Unit step

1/(1+Kp)

0

0

Unit ramp

Infinite

1/Kv

0

Unit parabolic

Infinite

Infinite

1/Ka

Kp is the positional error coefficient, \({K_p} = \mathop {\lim }\limits_{s \to 0} G\left( s \right)\)
Kv is the velocity error coefficient, \({K_v} = \mathop {\lim }\limits_{s \to 0} sG\left( s \right)\)
Ka is the acceleration error coefficient, \({K_a} = \mathop {\lim }\limits_{s \to 0} {s^2}G\left( s \right)\)
The steadystate error of a control system can be minimized by increasing the gain K.
Explanation:
Acceleration error constant is a measure of the steadystate error of the system when the input is parabolic function.
Positional error constant is a measure of the steadystate error of the system when the input is unit step function.
Velocity error constant is a measure of the steadystate error of the system when the input is ramp function.