Particle omission in embedded questions


Are there any rules or conventions on when to omit を (as in 1) or が (as in 2)
when it comes to embedded questions?

  1. この生物は何か教えてください。
  2. どれがおいしいかまずいかさっぱりわかりません。

My gut feeling would be to generalize and say that the particles are mostly
dropped in spoken /more casual language and kept in written/ more formal
language, but honestly I feel like I've seen them dropped relatively
frequently even in written language so I am unsure... Any thoughts?

