Questions

 It is a strange sequence. Each number describes the resemblance of the previous one, except the first one.

11 describes the previous '1' which contains one '1'

21 describes the previous '11' which contains two '1'

1211 describes the previous '21' which contains one '2' and one '1'

111221 describes the previous '1211' which contains one '1', one '2' and two '1'.

So the next sequence will be 312211, that is the previous '111221' contains three '1', two '2' and one '1'.

Among the given options, mud is not an aerosol.

An aerosol is a suspension of fine solid particles or liquid droplets, in the air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog, dust, forest exudates and geyser steam. Examples of anthropogenic aerosols are haze, particulate air pollutants, and smoke.

Frame relay is a packet switching technology. It will operate in the data link layer.

Data flow analysis studies the use of data on paths through the code.