Master of Orion II: Battle at Antares/Chemistry

The Chemistry techs appear in the 2nd row of the left column in the Research menu.

50 RP: Chemistry
This is a "general" tech level - even Uncreatives get all the techs. Ship Weapon that does 8 points of damage when it hits (eventually - it's the slowest missile as well as the weakest). Miniaturization: Reduces size and cost. Modifications: (0) EMG if you have that tech; (1) ARM, FST; (2) MIRV. Enables ships to travel go up to 4 parsecs from your nearest colony. All ships are fitted with your best Fuel Cells automatically, so in effect they do not increase a ship's production costs or reduce the space available for other components. Ship Special System that increases a ship's range by 50%, but requires quite a lot of space. The most basic grade of ship-building metal, known in many forums as "cardboard" or "tissue" because such ships are ridiculously fragile.
 * Nuclear Missile
 * Standard Fuel Cells
 * Extended Fuel Tanks
 * Titanium Armor

250 RP: Advanced Metallurgy
Enables ships to travel go up to 6 parsecs from your nearest colony. All ships are fitted with your best Fuel Cells automatically, so in effect they do not increase a ship's production costs or reduce the space available for other components. The range of existing ships is upgraded immediately and at zero cost. Twice as tough as Tritanium Armor; gives ground combat units a +10% bonus; makes missiles and fighters tougher. The first armor that's fit for combat.
 * Deuterium Fuel Cells
 * Tritanium Armor

Best choice for non-Creatives: this decision is a miniature research strategy in its own right, with separate paths for Tolerant and non-Tolerant races:
 * 1) For non-Tolerant races the key is that you will very soon need Merculite Missiles, as they are far better than Nuclear Missiles (especially if your opponent is Creative and soon gets Radiation Shield, which completely blocks all damage done by Nuclear Missiles; the hidden secret is that missiles do only 50% damage against planets, so Nuclear Missiles do 4 damage but Radiation Shield blocks 5, and their Missile Bases merrily pound your ships with effectively infinite ammunition); you can't afford to wait for the next-level missile (Pulson Missile). That means that, if your race is not Tolerant, you need Atmosphere Renewer for pollution control (Pollution Processor is half as effective as Atmosphere Renewer, and is in the same tech level as Merculite Missiles, so non-Creatives can't have both). So you can't have Iridium Fuel Cells (in the same tech level as Atmosphere Renewer) and therefore you need Deuterium Fuel Cells. All this means non-Tolerant non-Creatives take the risk of using Titanium Armor ("cardboard") until they research Zortrium Armor (higher up the Chemistry tech tree).
 * 2) Tolerant races need Merculite Missiles just as much, but they don't need any pollution control (unless they want to allow for conquering non-Tolerant colonies, in which case they follow route 1). So they usually take Iridium Fuel Cells later and Tritanium Armor now.

650 RP: Advanced Chemistry
Ship Weapon that does 14 points of damage when it hits (faster than Nuclear Missile). Miniaturization: Reduces size and cost. Modifications: (0) EMG if you have that tech; (1) ARM, FST; (2) MIRV. Type: Ship Independent Weapon Effect: 14 damage, exploding when target is reached. Miniaturization: Decreases space used. MIRV, Heavily Armoured, Fast, Emissions Guidance. Building that halves the effects of pollution.
 * Merculite Missile
 * Pollution Processor (80 PP; maintenance 1 BC)

Best choice for non-Creatives: Merculite Missile (see previous discussion).

1150 RP: Molecular Compression
Ship Weapon that does 20 points of damage when it hits (faster than Merculite Missile). Miniaturization: Reduces size and cost. Modifications: (0) EMG if you have that tech; (1) ARM, FST; (2) MIRV. Building that reduces effects of pollution by 75%. Cumulative with Pollution Processor (usually only Creatives get both), in which case pollution is reduced to 12.5%. Enables ships to travel go up to 9 parsecs from your nearest colony. All ships are fitted with your best Fuel Cells automatically, so in effect they do not increase a ship's production costs or reduce the space available for other components. The range of existing ships is upgraded immediately and at zero cost.
 * Pulson Missile
 * Atmospheric Renewer (150 PP; maintenance 3 BC)
 * Iridium Fuel Cells

Best choice for non-Creatives (see previous discussion):
 * For non-Tolerant races, Atmospheric Renewer.
 * For Tolerant races, Iridium Fuel Cells if they chose Tritanium Armor earlier; otherwise (if they took Deuterium Fuel cells earlier) they may choose either Iridium Fuel Cells or Pulson Missile.

2000 RP: Nano Technology
Achievement that halves the effects of pollution throughout the entire empire at zero cost. If a colony already has both Atmosphere Renewer and Polluiton Processor, the resulting level of pollution is 50% x 25% x 50% = 6.25%. Achievement that increases all workers' production by +1 throughout the empire at zero cost. Twice as tough as Tritanium Armor, 4 times as tough as Titanium Armor; gives ground combat units a +15% bonus; makes missiles and fighters tougher. With this armor your ships are tough enough for mid-game war, especially if you have Class 3 or better shields (in the Force Fields tech tree).
 * Nano Disassemblers
 * Microlite Construction
 * Zortrium Armor

Best choice for non-Creatives: Zortrium Armor.

This level is an important payday for Creatives: the "bonus techs" Nano Disassemblers and Microlite Construction make their workers almost as productive as a UniTol race's.

4500 RP: Molecular Manipulation
Ship Weapon, the most powerful and fastest missile; does 30 points of damage when it hits. Miniaturization: Reduces size and cost. Modifications: (0) EMG if you have that tech; (1) ARM, FST; (2) MIRV. The 2nd best armor you can research, 50% tougher than Zortrium; also gives ground combat units a bonus of +20%; makes missiles and fighters tougher. Enables ships to travel go up to 12 parsecs from your nearest colony. All ships are fitted with your best Fuel Cells automatically, so in effect they do not increase a ship's production costs or reduce the space available for other components. The range of existing ships is upgraded immediately and at zero cost.
 * Zeon Missile
 * Neutronium Armor
 * Uridium Fuel Cells

Best choice for non-Creatives: depends on your strategy and overall situation, as your earlier techs (Zortrium Armor; Merculite Missiles, now fully modified and miniaturized by 3 levels; Iridium Fuel Cells) are pretty good. Zeon Missiles are excellent if your ship are mainly armed with missiles, since Zeon Missile's speed makes it very difficult to shoot down most of a salvo; even if you prefer "beams", Zeon Missile make your Star Bases significantly more powerful. Uridium Fuel Cells can help you get at your opopnents, but if there's an uncolonized system halfway you could gamble by sending an Outpost Ship and hoping there's at least a Gas Giant or Asteroid Belt which will allow you to create an Outpost. Neutronium Armor is probably the least important in most cases.

10000 RP: Molecular Control
Enables ships to travel go an unlimited distance from your nearest colony. All ships are fitted with your best Fuel Cells automatically, so in effect they do not increase a ship's production costs or reduce the space available for other components. The range of existing ships is upgraded immediately and at zero cost. The best armor you can research, twice as tough as Zortrium; also gives ground combat units a bonus of +25%; makes missiles and fighters tougher.
 * Thorium Fuel Cells
 * Adamantium Armor

Best choice for non-Creatives: Adamantium Armor. The only better armor is Xentronium, which you can't research but may gain by beating Orion's Guardian or scrapping a captured Antaran ship (tactics that are often forbidden in multi-player games against human opponents), or by "obtaining" them from another player who has done one of these feats. If you're concerned about range, you should have chosen Uridium Fuel Cells at the previous level; galaxies in which Uridium Fuel Cells are insufficient are extremely rare.

Hyper-advanced Chemistry
Very useful if your main weapons are Zeon or even Pulson Missiles (large numbers of EMG FST ARM MIRV Zeon Missiles are a terrifying avalanche); otherwise not really useful.