1) 1F6888
1F₁₆ = 31₁₀
C is the 3rd character of the alphabet, while A is the 1st. Thus, 31 → Ca.
Carbon is atomic number 6, while Oxygen is atomic number 8.
1F → Ca
6 → C
888 → OOO
CaCOOO → CaCO3
2) 423 00 - 423 63
Both potentially Torslanda postcodes
Unsolved
3) EA3FE3CAA8D4591D2E11EC8E08692129
MD5 hash for 206888
Calcium atomic number 20
Carbon atomic number 6
Oxygen atomic number 8
CaCO3 again.
4) 57.1444 -4.9519 | 57.2182 -4.6180 | 44 12
57.1444. -4.9519 Coordinates near western end of River Moriston in Highland Council, UK
57.2182 -4.6180 Coordinates near eastern end of River Moriston in Highland Council, UK
44 12 is tap code for the letters “TB”, which has been interpreted to mean “Telford Bridge”, referring to the Invermoriston Bridge on River Moriston, built by Thomas Telford.
Telford was the “First President of the Institution of Civil Engineers” (source), aka ICE.
Civil Engineers → Cement → Calcium Carbonate
5) Snowflake
Ice → Calcium Carbonate
As water freezes, the dissolved minerals calcium and carbon solidify into tiny particles of calcium carbonate. (source)
6) Cross Cipher
Unsolved
This cipher can also be found in Robatama.
Note that mirroring across the horizontal axis results in matching symbols and filling in missing symbols; no conflicting symbols.