Which of the following methods is used to remove hardness from water?

What is formed when $PCl_3$ reacts with water?

$A$ coin and a six-faced die, both unbiased, are thrown simultaneously. The probability of getting a head on the coin and an odd number on the die is:

Which of the following is an accessory whorl of a flower?

An electron initially present in an excited state of $H$ atom is further excited to another energy level by an incident photon. It releases $10$ photons while coming back to the ground state,out of which $7$ have higher energy than the incident photon. The electron was initially present in

The cathode of a photoelectric cell is changed from a work function $W_1$ to $W_2$ $(W_2 > W_1)$. If the photoelectric currents before and after the change are $I_1$ and $I_2$ respectively,and all other conditions remain constant,then which of the following is true? (Assume $hv > W_2$)