Hope this helps :) remember your conversions and just practice it's fairly easy:)
The purpose of the uninoculated control tubes used in this test is that two uninoculated control tubes are needed to show the results of the medium in both aerobic and anaerobic environments. It is used to show it is sterile and also as a color comparison, used also to show that the medium remains green under both conditions.
The valence electrons are the parts of an atom that make interactions and make chemical bonds.
Every atom is made of three different components, a positively charged proton, neutrally charged neutron and negatively charged electron. The protons and the neutrons make up the atom's core and the electrons orbit around that core.
The electrons that orbit around the atom's core in its outer-most orbit (the one that is the furthest from the atom's core) can interact with electrons of other atoms, forming different kinds of chemical bonds.
If there is an exchange of the electrons (one atom donates its electrons to another atom), that results in forming of ions, then those two atoms can be linked in an ionic bond.
If an electron is shared between two atoms, then that bond is called a covalent bond.
