CREATE TABLE "table1_21350772_2" (
  "gas_name" text,
  "chemical_formula" text,
  "lifetime_years" text,
  "20_yr" text,
  "100_yr" text,
  "500_yr" text
);

Question: What is the 100 year for Carbon Dioxide?
SQL: SELECT "100_yr" FROM "table1_21350772_2" WHERE "gas_name"='Carbon dioxide';

Question: What is the 20 year for Nitrous Oxide?
SQL: SELECT "20_yr" FROM "table1_21350772_2" WHERE "gas_name"='Nitrous oxide';

Question: What is the lifetime (years) for chemical formula ch 4?
SQL: SELECT "lifetime_years" FROM "table1_21350772_2" WHERE "chemical_formula"='CH 4';

Question: What is the 500 year where 20 year is 289?
SQL: SELECT "500_yr" FROM "table1_21350772_2" WHERE "20_yr"='289';

Question: What is the 100 year when 500 year is 153?
SQL: SELECT "100_yr" FROM "table1_21350772_2" WHERE "500_yr"='153';

Question: What is the 20 year for Sulfur Hexafluoride?
SQL: SELECT "20_yr" FROM "table1_21350772_2" WHERE "gas_name"='Sulfur hexafluoride';