Since PQ is focal chord of the parabola y2=4ax
so let P(t2,2t), Q(t21,−t2) and R(3,0)

Given mPR⋅mPQ=−1
t2−32t×t21−3−t2=−1
(t2−1)2=0
⇒t=1
i.e. PQ must be the latus rectum
We get P(1,2)&Q(1,-2)
For ellipse
\frac{2{b}^{2}}{a}=4&ae=1
Also b2=a2(1−e2)
∴a=1+2
ande2=3−22
Hence e21=3−221=3+22