What type of plants are Pteridophytes?

The pair of compounds which cannot exist together in aqueous solution is
$I$. $NaH_2PO_4$ and $NaHCO_3$
$II$. $Na_2CO_3$ and $NaHCO_3$
$III$. $NaOH$ and $NaH_2PO_2$
$IV$. $NaHCO_3$ and $NaOH$

If a line makes angles $\tan ^{-1} \sqrt{7}$ and $\tan ^{-1} \frac{\sqrt{5}}{\sqrt{3}}$ with the $X$-axis and $Y$-axis respectively,then the angle made by it with the $Z$-axis is

The value of $k$,if $(1,2)$ and $(k,-1)$ are conjugate points with respect to the ellipse $2x^2 + 3y^2 = 6$ is:

Two bodies $A$ and $B$ start from the same point at the same instant and move along a straight line. $A$ moves with uniform acceleration $a$ and $B$ moves with uniform velocity $V$. They meet after time $t$. The value of $t$ is:

What is considered a species?