Which one of the following is an example of cleistogamy?

The oxide of a metal contains $40 \%$ of oxygen. The valency of the metal is $2$. What is the atomic weight of the metal?

Assertion : In plant tissue culture,somatic embryos can be induced from any plant cell.
Reason : Any viable plant cell can differentiate into somatic embryos.

$A$ plane is parallel to two lines whose direction ratios are $(1, 0, -1)$ and $(-1, 1, 0)$ and it contains the point $(1, 1, 1)$. If it cuts the coordinate axes at $A$,$B$,and $C$,then the volume of the tetrahedron $OABC$ is (in cubic units):

An infinitely long straight conductor is bent into the shape as shown below. It carries a current of $I$ ampere and the radius of the circular loop is $R$ metre. Then,the magnitude of magnetic induction at the centre of the circular loop is

What type of polymer is natural rubber?