Assertion (A): When plane of coil is perpendicular to magnetic...

According to faraday's law of induction, induced $\text{emf}e = - \dfrac{d ϕ}{d t}$

$ϕ$is the magnetic flux linkage with the coil it is defined as, $ϕ = \overset{\to}{B} \cdot \overset{\to}{∆ s}$or $ϕ = B ∆ scos\theta,$here, $\theta$is the angle between the magnetic field vector and area vector, therefore, when $\theta = 0 ° , ϕ$has maximum value and for $\theta = 90 ° , ϕ$has minimum value.

Thus, when plane of coil is perpendicular to magnetic field, magnetic flux linked with the coil is minimum, therefore induced emf is zero.