For the primary question, the appropriate response is natural. A natural sign wipes out every single material inadvertent in that bar and additionally accidentals in the key mark. In any case, on account of the key mark accidentals, the common sign is just relevant to that bar.
For the second question, the appropriate response is ritard. Ritard is an abbreviated variant of the word ritardando, which is a term utilized as a part of music to allude to step by step turning out to be slower.