The correct equation is option c.
To find the moment of inertia of the system of three point masses about an axis passing through one of the corners and perpendicular to the plane of the triangle, you can use the parallel axis theorem and treat each mass as a point mass.
Moment of inertia of each of the point masses (m) at B and C about the side BC= m(0)2 = 0.
Moment of inertia of point mass m at A about the side BC = m(AD)².
Now, AD = I sin 60°
1 √3 /2 -(height of equilateral triangle)
.. Moment of inertia of the system about side BC
=0+0+m = (1 √3 /2))²
3ml)²/ 4