Chitin is an example of which of the following?

$A$ diode having a potential difference of $0.5\,V$ across its junction,which does not depend on the current,is connected in series with a resistance of $20\,\Omega$ across a source. If $0.1\,A$ current passes through the resistance,what is the voltage of the source (in $,V$)?

Maximum amount of oxygen is exchanged from the blood at the . . . . . . .

The equations of the circle which pass through the origin and make intercepts of lengths $4$ and $8$ on the $x$ and $y$-axes respectively are

Which of the following is not a synthetic polymer?

The sugar present in milk is