One mole of calcium phosphide on reaction with excess water gives

An aeroplane flying with uniform speed horizontally $1 \ km$ above the ground is observed at an elevation of $60^{\circ}$. After $10 \ s$,if the elevation is observed to be $30^{\circ}$,then the speed of the plane (in $km/h$) is

In the Davisson-Germer experiment, an electron beam of energy $75 \ eV$ falls normally on the surface of a crystal. If the maximum intensity is obtained at an angle of $45^{\circ}$ to the direction of the incident beam, then the inter-atomic distance in the lattice plane of the crystal will be :-............... $\mathring{A}$

The perimeter of a sector is a constant. If its area is to be maximum,the sectorial angle is:

An ideal gas expands isothermally from a volume $V_1$ to $V_2$ and is then compressed to the original volume $V_1$ adiabatically. The initial pressure is $P_1$ and the final pressure is $P_3$. If the total work done is $W$,then:

Which of the following can be used to extinguish a fire caused by alkali metals?