**fill in the blanks**

according to one theory, earth’s moon accreted to form its current structure following a giant impact between earth and another celestial body. complete the paragraph to describe the process of accretion.

following the impact, a section of earth broke off. as a result, large pieces of debris started to revolve around earth. the debris was held close to earth by earth’s the debris frequently collided to form a planetesimal. as the planetesimal grew in size, its gravity increased. this gravitational force pulled in even more , which led to the accretion of the moon.

**first blank options**
1) atmosphere
2) rotational motion
3) gravity
4) oceans

**second blank options**
1) matter
2) gravity
3) atmosphere
4) theories

Word for the first blank: gravity

Word for the second blank: matter

Explanation:

The only way debris from the impact with Earth can be held close to Earth is due to a force. The only force that could be acting from Earth is "the force of gravity".

The gravitational pull of this new object being formed, increases proportional to its mass as more and more "matter" accumulates. And the accretion process is now on its way.

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.

are there options? cause you ain’t. real specific