Questions

Africa is the second largest continent both by popolation and area wise. Asia being first by both popolation and area wise.

In flowering plants one sperm nucleus fertilizes the egg and the other sperm nucleus fuses with two other nuclei found within the ovule, thus forming triploid endosperm.

Hence, double fertilization is unique to flowering plants.

Robert Brown, Scottish botanist, Discovered The Nucleus of a Cell in 1831, London. When Brown was studying orchids under microscope when he observed an opaque area, which he called the "Areola" or "Nucleus", in the cells of the flower's outer layer.

The nucleus was also described by Franz Bauer in 1804 but in detail Robert Brown made it in 1831.

Isthmus of panama and Isthmus of Suez are well known examples

Let the required number be 'X'

Condition 1 :  

$$\begin{gathered} XX = 2X \\ => 2X2 = X \\ => X = 12 \end{gathered}$$

Condition 2 :

$$\begin{gathered} X × X = X2 \\ => X = 12 \end{gathered}$$

Therefore, 12 is the number which becomes double when it is divided by itself and becomes half when it is multiplied by itself.

The highest of this peak is 1772 m.