Some Basic Concepts Of Chemistry

Moles of = mol
Mg reacts in stoichiometric ratio with , calculate mass = moles molar mass

Bond orders: So the decreasing order is:

Law of definite proportions states that a given compound always contains the same elements in the same proportion by mass, regardless of the source.
In water (H\textsubscript{2}O), the mass ratio of hydrogen to oxygen is always fixed.

- Molecules with incomplete octet: BeH2 and BC13 have incomplete octets, so this pair is correct.
- Polar molecules: BF3 is a non-polar molecule due to its symmetrical triangular shape, while CCl4 is also non-polar. Hence, the pair is incorrect.
- Molecules with expanded octet: PCl5 and SF6 both have expanded octets, so this pair is correct.
- Odd electron molecules: NO and NO2 are odd electron molecules, so this pair is correct.
Thus, the incorrectly matched pair is .

- Sodium chlorate and sodium arsenite are used as herbicides.
- DDT and Aldrin are insecticides.
- Nicotine is a natural insecticide.