Which of the following guards the opening of the hepatopancreatic duct into the duodenum?

Assertion $(A)$: Ductile metals are used to prepare thin wires.
Reason $(R)$: In the stress-strain curve of ductile metals, the length between the points representing elastic limit and breaking point is very small.

In an experiment on photoelectric emission from a metallic surface,the wavelength of incident light is $2 \times 10^{-7} \ m$ and the stopping potential is $2.5 \ V$. The threshold frequency of the metal (in $Hz$) is approximately (charge of electron $e = 1.6 \times 10^{-19} \ C$,Planck's constant $h = 6.6 \times 10^{-34} \ J \cdot s$):

The transfer of energy from organism to organism in a natural community establishes

The reagent used in the Wolff-Kishner reduction is

The least positive integer $n$ for which $(1+i)^n=(1-i)^n$ is