Which of the following pairs is incorrectly matched?

$A$ ball is thrown on a lawn in such a way that it initially slides with a speed $v_0$ without rolling. It gradually picks up rotational motion. Find the speed of the ball at which there will be rolling without slipping.

Which one of the following transitions of an electron in a hydrogen atom emits radiation of the lowest wavelength?

If the angles of dip at two places are $30^o$ and $45^o$ respectively,then the ratio of horizontal components of earth's magnetic field at the two places will be

Two circular coils can be arranged in any of the three situations shown in the figure. Their mutual inductance will be

$y=A e^x+B e^{2 x}+C e^{3 x}$ satisfies the differential equation