To obtain the truth-table shown, from the following logic circuit, the gate G should be

An electric dipole consisting of two opposite charges of $$2 \times 10^{-6} \mathrm{C}$$ separated by a distance of $$3 \mathrm{~cm}$$ placed in an electric field of $$2 \times 10^5 \mathrm{~N} / \mathrm{C}$$ then the maximum torque acting on dipole is

In insulators

Seven identical discs each of mass $$M$$ and radius $$\mathrm{R}$$ are arranged in a hexagonal plane pattern so as to touch each neighbour disc as shown in the figure. The moment of inertia of the system of seven discs about an axis passing through the centre of central disc and normal to the plane of all discs is