What is the correct order of processes in the accretion of planetesimals?

A). Collapse, condensation, accretion, clearing.

Explanation:

Planetesimals are described as the small solid astronomical objects which are the building blocks for the formation of solid planets. Accretion is described as the process in which the solid astronomical objects cluster to form larger objects that eventually leads to the formation of planets.

As per the question, the correct order of processes that are followed in this accretion process would be a collapse, condensation, accretion, clearing. First occurs the collapse of a nebula followed by condensation of cosmic dust grains. After this, the accession or accumulation of solid parts takes place to form larger objects and this is immediately followed by the clearing of debris and dust to allow planets to form. Thus, option A is the correct answer.

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.