Focal length of a convex lens will be maximum for

The area (in square units) of the circle which touches the lines $4x + 3y = 15$ and $4x + 3y = 5$ is

Two spheres of the same material have radii $1\ m$ and $4\ m$ and temperatures $4000\ K$ and $2000\ K$ respectively. The ratio of the energy radiated per second by the first sphere to that by the second is

Bird flu is caused by

In the given columns, column $I$ contains the terms and column $II$ contains their descriptions. Select the correct match from the options given below.

Column $I$	Column $II$
$A$. Growth	$I$. Production of offspring.
$B$. Reproduction	$II$. Composed of one or more cells.
$C$. Metabolism	$III$. Increase in mass and increase in number of individuals.
$D$. Cellular organization	$IV$. Sum total of all chemical reactions occurring in the body.

If from a point $P(a, b, c)$ perpendiculars $PA$ and $PB$ are drawn to $yz$ and $zx$ planes respectively,then the equation of the plane $OAB$ is