If $\vec{P} \cdot \vec{Q} = PQ$,then the angle between $\vec{P}$ and $\vec{Q}$ is ............. $^\circ$.

$A$ photon collides with a stationary hydrogen atom in the ground state inelastically. The energy of the colliding photon is $10.2 \, eV$. After a time interval of the order of a microsecond,another photon collides with the same hydrogen atom inelastically with an energy of $15 \, eV$. What will be observed by the detector?

When a certain weight is suspended from a long uniform wire,its length increases by $1 \ cm$. If the same weight is suspended from another wire of the same material and length but having a diameter half of the first one,the increase in length will be ......... $cm$.

With an increase in atomic number,the melting point of alkali metals .......

What are plasmodesmata?

The coconut water and the edible part of coconut are equivalent to: