When $NaCl$ is dissolved in water,the sodium ion becomes

If the direction cosines of two lines are such that $l+m+n=0$ and $l^2+m^2-n^2=0$,then the angle between them is:

If $D, E$ and $F$ are respectively the mid-points of $AB, AC$ and $BC$ in $\triangle ABC$,then $\overrightarrow{BE} + \overrightarrow{AF}$ is equal to :

The angle between the lines represented by $y^2 \sin^2 \theta - xy \sin^2 \theta + x^2(\cos^2 \theta - 1) = 0$ is

Which of the following equations is a balanced one?

$X -$ In deep-sea hydrothermal vents,the average temperature is significantly higher than $25$ to $30^{\circ} C$.
$Y -$ Reptiles and amphibians are ectotherms (poikilotherms),not eurythermal.