All wires have the same resistance $r$. The equivalent resistance between $A$ and $B$ is $R$ when the keys $K_1$ and $K_2$ are open. Now,if the keys are closed,what will be the new equivalent resistance?

Which was the first inorganic pesticide developed on a commercial scale?

Shreya read in her textbook that communicable diseases are caused by pathogens. These pathogens pass from patients to healthy persons causing the disease. She suggested her friends that we can prevent the spread of these diseases and even some of them can be eradicated.

$(a)$ What are the various methods of spread of communicable diseases?

$(b)$ What preventive measures can be taken to prevent the spread of communicable diseases?

$(c)$ Which values are displayed by Shreya in taking initiative ?

$(d)$ Suggest some school activity to promote such values in school students ?

The displacement-time equation of a particle executing $SHM$ is $x = A \sin \left( \omega t + \frac{\pi}{6} \right)$. The time taken by the particle to go directly from $x = -\frac{A}{2}$ to $x = +\frac{A}{2}$ is

Chloroethane reacts with $X$ to form diethyl ether. What is $X$?

Match the following elements of the matrix $A = \begin{bmatrix} 1 & -1 & 0 \\ 0 & 4 & 2 \\ 3 & -4 & 6 \end{bmatrix}$ with their co-factors and choose the correct answer.

Element	Co-factor
$A$. $-1$	$(1)$ $-2$
$B$. $1$	$(2)$ $32$
$C$. $3$	$(3)$ $4$
$D$. $6$	$(4)$ $6$
	$(5)$ $-6$