Which of the following is a chemical reaction?

a. making a hydrogen bond between a water molecule and a sugar molecule.
b. the melting of ice.
c. changing a carbon atom to a nitrogen atom by radioactive decay.
d. the formation of a covalent bond between two amino acids

d. The formation of a covalent bond between two amino acids

Explanation:

In a chemical reaction, a substance transforms into another with different chemical properties and a different formula. Bonds are created and/or destroyed. It must obey the law of conservation of mass and the law of conservation of elements.

Which of the following is a chemical reaction?

a. Making a hydrogen bond between a water molecule and a sugar molecule. NO. This is a physical change in which sugar dissolves in water but both their chemical identities remain the same. The hydrogen bond is a force of  attraction and not a real bond in which electrons are gained, lost or shared.

b. The melting of ice. NO. This is a physical change. Solid water turns into liquid water but the identity of the molecules is the same.

c. Changing a carbon atom to a nitrogen atom by radioactive decay. NO. This is a nuclear reaction in which a new element appears but it is not a chemical reaction because it does not fulfill the law of conservation of elements.

d. The formation of a covalent bond between two amino acids. YES. A new bond is created and a protein dimer is formed.

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answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).