Explain as to why two hydrogen form H2 molecule but not molecules such as H3, H4 etc..​

Hydrogen is a diatomic gas with two atoms (di meaning two). H2 is referred to as molecular hydrogen because hydrogen atoms are covalently joined together to form a molecule.

Because two hydrogen molecules are connected to one other by a covalent connection, hydrogen is denoted as H2.

Hydrogen has only one electron, so to complete its duet(octet in case of nitrogen) it has to bond with another hydrogen molecule to be stable and also exist.

You can remember it like this :

H = element

H2 = gas

Other diatomic gases :

O2 (oxygen)

N2 (nitrogen)

there is none because earth is stationary and flat.

the transfer of heat by electromagnetic radiation is called thermal radiation . it is usually carried out by electromagnetic waves in an energy range just below the visible spectrum, which is the infrared range.

so the answer would be radiation.

: )