Question 25 2.5 pts
Which of the following statements describes a difference
between a chemical change and a physical change in a
substance?
Tim
Attei
231
o The result of a chemical change is a different
composition; in a physical change, the composition
remains the same.
o A physical change occurs only in elements: a
chemical change occurs only in compounds.
O A chemical change occurs only in elements; a
physical change occurs only in compounds.
The result of a physical change is a different

o The result of a chemical change is a different  composition; in a physical change, the composition  remains the same.

Explanation:

In a chemical change, new kinds of matter are produced although the atoms are the same.

For physical changes, no new kinds of matter formed. Only the state of substances changes.

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.