Occasionally, a C¬H group can form a hydrogen bond. Why would such a group be more likely to be a hydrogen bond donor group when the C is next to N

Check explanation.(Last paragraph).

Explanation:

Hydrogen bond was used to account for the Behavior of some organic compounds containing Electronegative elements such as nitrogen and oxygen. It was proposed that, '' when a Hydrogen atom lies between two highly Electronegative atoms, it shows a unique property of forming a bond between them by holding one of the atoms by a covalent bond and the other by purely electrostatic force''. This electrostatic force is known as the hydrogen bonding.

===> So, let us now answer the question properly; C- H group would be more likely to be a hydrogen bond donor group when the C is next to N because their would be separation of charge in the adjacent C-H bond which is caused by the positively charged Nitrogen (N). This will cause a C^- and a H^+, that is partial negative and positive charges on carbon and Hydrogen respectively. With this, the ease at which hydrogen will donate will increase.

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

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.