CREATE TABLE table_2576 ("No. in series" TEXT, "No. in season" TEXT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( millions ) " TEXT)

What episode number in the series was 'igo nuclear'?
SELECT "No. in season" FROM table_2576 WHERE "Title" = 'iGo Nuclear'
SELECT "No. in season" FROM "table_2576" WHERE "Title" = 'iGo Nuclear'