Which phase of the cell cycle is characterized by the replication of $DNA$ and the synthesis of histone proteins?

$A$ certain metallic surface is illuminated with monochromatic light of wavelength $\lambda$. The stopping potential for the photoelectric current for this light is $3V_0$. If the same surface is illuminated with light of wavelength $2\lambda$,the stopping potential is $V_0$. The threshold wavelength for this surface for the photoelectric effect is:

If a curve $y = a\sqrt{x} + bx$ passes through the point $(1, 2)$ and the area bounded by the curve,the line $x = 4$,and the $x$-axis is $8$ sq. units,then:

Read the following statements carefully and select the correct statements.
$(1)$ The wheat variety $Atlas-66$ has high protein content.
$(2)$ $SCP$ is an alternative source of protein for human and animal nutrition.
$(3)$ Plants developed through micropropagation are genetically different from the parent plant.
$(4)$ Semi-dwarf rice varieties were developed from $IR-8$ and $Taichung Native-1$.

Which of the following metals is a water pollutant and causes sterility in human beings?

$\operatorname{cosec} 15^{\circ} + \sec 15^{\circ}$ is equal to :