The correct option is C 40.2 J mol−1
Van't Hoff equation is
log10K=−△Ho2.303 RT+logC
where C is a constant.
Graph between log10K and 1T is linear.
On comparing it to
y=mx+c
slope, m=−△Ho2.303 R .....1
but, slope m also equals,tan θ
since θ=tan−1(−2.1)
So,
slope, m=tan θ=−2.1 ......2
comparing equation 1 and 2 , we get
−△Ho2.303 R=tan θ
putting the values we get,
∴ △Ho=2.303 R×2.1
=2.303×8.314×2.1=40.2 J mol−1.