Which of these is not a mixture? a) baking soda b) salt and water c) iron filings and sand d) metal paper clips and plastic paper clips

Baking Soda

Explanation:

Baking soda is not a mixture but a chemically bonded compound which is a result of the reaction between Sodium and the carbonate anion with the following chemical formula .In a mixture there are no fixed proportions of the substances involved and the substances keep their physical properties and with most mixtures the substance can be separated from each other mechanically.However a mixture of salt and water is known as a homogeneous mixture meaning the salt can no longer be seen separate in the solution but uniformly dissolves in the water.

Uracil is the nitrogenous base that exists in RNA but is absent in DNA.

Explanation:

Uracil or uracil is a nitrogenous base. Represented by the letter U in the genetic code, it is a simple, pyrimidine ring base capable of making two hydrogen bonds, just like thymine. It replaces thymine in DNA to RNA transcription to complement adenine. It is an exclusive base of RNA, that is, it does not occur in DNA.