When zeolite,which is a hydrated sodium aluminium silicate,is treated with hard water,the sodium ions are exchanged with which of the following?

$A$ photon of energy $E$ ejects a photoelectron from a metal surface whose work function is $W_0.$ If this electron enters into a uniform magnetic field of induction $B$ in a direction perpendicular to the field and describes a circular path of radius $r,$ then the radius $r$ is given by (in the usual notation):

Which kingdom is characterized by the presence of a rigid cell wall and nucleoprotein as genetic material?

The colour of the bead in the borax bead test is mainly due to the formation of:

If the acceleration due to gravity at the Earth is $g$,the mass of the Earth is $80$ times that of the Moon,and the radius of the Earth is $4$ times that of the Moon,then the value of the acceleration due to gravity at the surface of the Moon will be:

In the circuit,if the forward voltage drop for the diode is $0.5\, V$,the current will be.......$mA$.