Questions

Both flies and bees can sit on the uncovered food and contaminate the food.

Saw dust contains carbon which is oxidised to carbon  dioxide by concentrated nitric acid;

PWC refers to Personal Water Crafts.

To control steering on a PWC, the most needed requirement is to have power in which will allows the one using it to control the engine for it to stop or for it to move. Without power, the person using it could be out of balance or fail to start the engine. This is the basic requirement because even though it is shut off or the engine is off, the PWC is still on and it could still move without proper knowledge of the engine.

Edit the ad associated with that keyword and direct users to a landing page that is very relevant.

Among the given options Brass is not a compound. Since it is an alloy, it is a mixture. It is a mixture of copper and zinc.

The smallest part of a compound is called a molecule. It has a unique composition that is always the same.

Compound is a substance that consists of two or more elements. 

   1) SO2                  2) CH2Cl2                3) PCl3

How to check the given molecules are polar or non polar :

If the electronegativity of the two bonded atoms are different then the bond is polar. Although, some molecules contain polar bonds, the molecule may be non-polar. If the polarity of all the bonds present in the molecule are cancel each other then molecule is non-polar.

In the given options,

SO2  is polar because the dipole moments on the O do not cancel.

PCl3  is polar because the P-Cl bonds do not cancel out.

CH2Cl2  polar because the C-Cl bonds do not cancel.

Hence, in brief, Polar molecules are molecules with net dipole due to the presence of partial positive and partial negative charge.

For example, water is a polar molecule that has partial positive and partial negative charge on it. CO2 is a non polar compound.

Therefore, all the given options SO2, CH2Cl2 and PCl3 are Polar molecules.