Two changes are described below. a. ice melts to form water. b. sugar cubes dissolve in hot coffee. which statement is true about the two changes? a. both are chemical changes because there is a change in the composition of ice and sugar. b. both are physical changes because there is a change in the physical states of ice and sugar. c. a is a physical change due to a change of state, but b is a chemical change because new molecules are formed. d. a is a chemical change due to a change of state, but b is a physical change because new molecules are formed.

Option (b) is the correct answer.

Explanation:

A change that does not lead to any difference in chemical composition of a substance is known as a physical change.

For example, shape, size, mass, volume, density, boiling point, etc of a substance are all physical properties.

As ice melts to form water shows that only the state of matter is changing. Hence, it is a physical change. Similarly, sugar cubes dissolve in hot coffee is also a physical change as no new compound has formed.

On the other hand, changes that lead to bring change in chemical composition of a substance is known as a chemical change.

For example, exploding dynamite, rotting cheese etc are all chemical changes.

Thus, we can conclude that both are physical changes because there is a change in the physical states of ice and sugar.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

it's c. elements are placed in rows based on how may valencies electrons have.