Which system of classification is used by most of the world's well-known herbaria?

$A$ liquid does not wet the solid surface if the angle of contact is

$A$ Carnot engine whose low temperature reservoir is at $7^{\circ} C$ has an efficiency of $50 \%$. It is desired to increase the efficiency to $70 \%$. By how many degrees should the temperature of the high temperature reservoir be increased? (in $K$)

$A$ student connects a long air-cored coil of manganin wire to a $100\, V$ $D.C.$ supply and records a current of $25\, A$. When the same coil is connected across a $100\, V$,$50\, Hz$ $A.C.$ supply,the current reduces to $20\, A$. The reactance of the coil is ...... $\Omega$.

Two capacitors $C_1$ and $C_2$ in a circuit are joined as shown in the figure. The potential of point $A$ is $V_1$ and that of $B$ is $V_2$. The potential of point $D$ will be

Identify the pair of viral diseases.