The colour of the bead in the borax bead test is mainly due to the formation of:

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

$A$ group of species with a common ancestor is known as:

$A$ student has to answer $10$ out of $13$ questions in an examination,choosing at least $5$ questions from the first $6$ questions. The number of choices available to the student is:

The image of the pair of lines represented by $ax^2 + 2hxy + by^2 = 0$ by the line mirror $y = 0$ is

$A$ particle starting from the origin $(0, 0)$ moves in a straight line in the $(x, y)$ plane. Its coordinates at a later time are $(\sqrt{3}, 3)$. The path of the particle makes an angle of $.......^{\circ}$ with the $x$-axis.