Based on it physical properties is a colloid a homogeneous mixture or heterogenous mixture? how does it differ from a solution?

Colloid is homogeneous mixture.

In solution the particle size is less than one nm. While particles in colloid are larger than solution particles.  When light pass through solution it can not scatter the light.

Explanation:

Colloidal:

Colloid consist of the particles having size between 1 - 1000 nm i.e, 0.001- 1μm.  

The particles in colloid can not be seen through naked eye.

It is homogeneous.

We can not separate the colloidal through the filtration. The pore size of filter paper is 2μm. However it can be separated through the ultra filtration. In ultra filtration the pore size is reduced by soaking the filter paper in gelatin and then in formaldehyde. This is only in case of when solid colloidal is present, if colloid is liquid , there is no solid particles present and ultra filtration can not be used in this case.

In solution the particle size is less than one nm. While particles in colloid are larger than solution particles.  When light pass through solution it can not scatter the light.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.