Which of the following reagents is used in the Gatterman-Koch formylation of arene?

Using the Trapezoidal rule,find the approximate value of $\int_1^4 y \, dx$ based on the following table:

$x$	$1$	$2$	$3$	$4$
$y$	$0.7111$	$0.7222$	$0.7333$	$0.7444$

(in $.1833$)

As the switch $S$ is closed in the circuit shown in the figure,the current passing through it is ................ $A$.

If the earth were to suddenly contract to $\frac{1}{n}^{th}$ of its present radius without any change in its mass,then the duration of the new day will be:

$NaOH$ is prepared by which of the following methods?

The Vernier scale of a travelling microscope has $50$ divisions which coincide with $49$ main scale divisions. If each main scale division is $0.5 \text{ mm}$,then the least count of the microscope is