Which of the following complex ions exhibits optical isomerism? ($en = 1,2$-diaminoethane)

If $2 x^2-3 x y+y^2+x+2 y-8=0$, then $\frac{d y}{d x}$ is equal to

The number of possible enantiomeric pairs that can be produced on monochlorination of $2$-methylbutane is

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 ?

Identify the organism shown in the given figure.

The period of $\sin ^4 x + \cos ^4 x$ is