Which orbital is dumb-bell shaped?

The electronic configuration of $Yb^{2+}$ is:

The image of the line $x+y-2=0$ in the $y$-axis is

$A$ metal rod of length '$l$' rotates about one of its ends in a plane perpendicular to a magnetic field of induction '$B$'. If the e.m.f. induced between the ends of the rod is '$e$',then the number of revolutions made by the rod per second is

When $NaCl$ is dissolved in water,the sodium ion becomes

Two identical piano wires have a fundamental frequency of $600 \text{ Hz}$ when kept under the same tension. What fractional increase in the tension of one wire will lead to the occurrence of $6 \text{ beats per second}$ when both wires vibrate simultaneously?