The colour of the X2 molecules of group 17 elements changes gradually from yellow to violet down the
group. This is due to


[A] the physical state of X2 at atom temperature changes from gas to solid down the group


[B] decrease in HOMO-LUMO gap down the group


[C] decrease in  gap down the group


[D] decrease in ionization energy down the group

Rahul Kumar Chemistry 30 Dec, 2017 1 Answer 453 views




























(A) In the region 0 < r < R, the magnetic field is non-zero (B) In the region R < r < 2R, the magnetic field is along the common axis. (C) In the region R < r < 2R, the magnetic field is tangential to the circle of radius r, centered on the axis. (D) In the region r > 2R, the magnetic field is non-zero.

Ritesh Rai Physics 10 Dec, 2017 1 Answer 382 views

In a triangle PQR, P is the largest angle and cos P = 1/3. Further the incircle of the triangle touches the sides PQ, QR and RP at N, L and M respectively, such that the lengths of PN, QL and RM are consecutive even integers. Then possible length(s) of the side(s) of the triangle is (are) ?

Devendra Yadav Maths 10 Dec, 2017 1 Answer 551 views



Words of length 10 are formed using the letters, A, B, C, D, E, F, G, H, I, J. Let x be the number of such words where no letter is repeated ; and let y be the number of such words where exactly one letter is repeated twice and no other letter is repeated. Then, y/9x=?

Devendra Yadav Maths 10 Dec, 2017 1 Answer 1937 views

A stationary source emits sound of frequency f0 = 492 Hz. The sound is reflected by a large car approaching the source with a speed of 2 m/s . The reflected signal is received by the soruce and superposed with the original. What will be the beat frequency of the resulting signal in Hz? (Given that the speed of sound in air is 330 m/s and the car reflects the sound at the frequency it has received).

Devendra Yadav Physics 10 Dec, 2017 1 Answer 710 views