How many chloride ions are there around a sodium ion in a sodium chloride crystal?

Which of the following compound$(s)$ has '$Z$' configuration?

The wavelength of the light used in Young's double slit experiment is $\lambda$. The intensity at a point on the screen is $I$,where the path difference is $\lambda/6$. If $I_0$ denotes the maximum intensity,then the ratio of $I$ and $I_0$ is

Which of the following radioisotopes is used as anticancerous?

Observe the following statements :
$I$. The circle $x^2+y^2-6x-4y-7=0$ touches the $y$-axis.
$II$. The circle $x^2+y^2+6x+4y-7=0$ touches the $x$-axis.
Which of the following is a correct statement?

$A$ $DC$ source with internal resistance $R_0$ is connected to three identical resistors,each of resistance $R$,as shown in the figure. If the thermal power generated in the circuit is highest,then