Which amino acids are present in histones?

Ionic radius (in $\mathring{A}$) of $As^{3+}$,$Sb^{3+}$ and $Bi^{3+}$ follow the order

A $6 \, V$ cell with $0.5 \, \Omega$ internal resistance, a $10 \, V$ cell with $1 \, \Omega$ internal resistance and a $12 \, \Omega$ external resistance are connected in parallel. The current (in ampere) through the $10 \, V$ cell is

$A$ Zener diode,having a breakdown voltage equal to $15 \, V$,is used in a voltage regulator circuit as shown in the figure. The current through the diode is ..... $mA$.

Which of the following is/are barbiturates?

Bond energy of covalent $O-H$ bond in water is