If a convex lens of focal length $80 \ cm$ and a concave lens of focal length $50 \ cm$ are combined together,what will be their resulting power?

In which of the following is the $P - O - P$ bond present?

Which of the following halogens has the highest bond dissociation energy?

Which of the following has the maximum boiling point?

Manganese is required in

$A$ wheel with ten metallic spokes,each $0.50 \ m$ long,is rotated with a speed of $120 \ rev/min$ in a plane normal to the earth's magnetic field at the place. If the magnitude of the field is $0.4 \ G$,the induced $e.m.f.$ between the axle and the rim of the wheel is equal to: