If $A$ is a $3 \times 4$ matrix and $B$ is a matrix such that $A'B$ and $BA'$ are both defined,then $B$ is of the type:

The angle between the lines whose direction cosines satisfy the equations $l+m+n=0$ and $l^2+m^2-n^2=0$ is

If the direction ratios $(l, m, n)$ of two lines satisfy the equations $l+m+n=0$ and $mn-2ln+lm=0$,then the angle between the lines is

The complete hydrolysis of $ICl , ClF _3$ and $BrF _5$, respectively, gives

Hydrolysis of $NCl_3$ gives $NH_3$ and $X$. Which of the following is $X$?

When radiation of the wavelength $\lambda$ is incident on a metallic surface,the stopping potential is $4.8 \ V$. If the same surface is illuminated with radiation of double the wavelength,then the stopping potential becomes $1.6 \ V$. Then,the threshold wavelength for the surface is: