general factss from p block which can be asked in various entrance xam..

1. I₂ can be dissove in- KI but not in NaI.

2. correct order of electron gain enthalpy of halogens- I>Br>F> Cl.

3. the formula of mineral borax is Na₂B₄O₇.10H₂O

4. the product obtained at anode when 50% H₂SO₄ aq solution is electrolyse using platinum electrodes is H₂S₂O₈ and not H₂SO₃

a ray incident on a plane mirror. for what angle of incident the ray wll undergo deviation of 4pi/5 radian???

hii...

focal length of concave mirror is independent of the medium which surrounds it. while the focal length of any lens, whether concave or conex, depends upon the medium surrounding it....

further by lens maker's formula, 1/f=(n-1)(1/R1-1/R2) focal length of any lens is inversly proportional to the refractive index, therefore the focal length of the concave lens will decrease when we place the latter from air to water as the medium as the refractive index of water is more than the refractive index of air.