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nacl is an ionic solid. the na+ and cl− ions in nacl are bonded through an electrostatic force of attraction commonly known as the ionic bond. water is a polar solvent. the oxygen atom, being more electronegative, attracts the electron cloud toward itself. as the electron cloud is pulled by the oxygen atom, it carries a partial negative charge, and the hydrogen atoms carry a partial positive charge. this partial separation of charges in the water molecule makes it polar. predict which intermolecular forces contribute the most to the dissolution of nacl in water. check all that apply.
a. ion-ion forces
b. ion-dipole forces
c. dipole-dipole forces
d. hydrogen bonding
suppose that nacl is added to hexane (c6h14) instead of water. which of the following intermolecular forces will exist in the system?
a. ion-dipole force between na+ ions and a hexane molecule
b. ion-ion force between na+ and cl− ions
c. dipole-dipole force between two hexane molecules
d. hydrogen bonding between na+ ions and a hexane molecule
e. london dispersion force between two hexane molecules

NaCl and water: Ion - Dipolo forces

NaCl and Hexane: Ion-ion force between Na+ and Cl− ions and London dispersion force between two hexane molecules

Explanation:

NaCl and water:

The ion-dipole force is established between an ion and a polar molecule.  Polar molecules are dipoles, they have a positive end and a negative end.

H2O has an important charge separation in its atoms (the H has a positive partial charge and the O has a negative partial charge) and this causes permanent electrical dipoles in the water molecules.

Sodium chloride is an ionic compound formed of positive and negative charge ions, Na + and Cl-. Depending on their charge, these ions will be attracted to opposite charges in the water molecules (H attracts chloride ions and O attracts sodium ions), causing the salt to dissolve in water.

NaCl and Hexane:

The dispersion forces of London occur between apolar molecules, and they occur because when two molecules approach a distortion of the electronic clouds of both originates, generating in them, transient induced dipoles, due to the movement of the electrons, so it allows interact with each other.

Hexane is a non-polar molecule, which are those that have no charge separation within the molecules. Then there is London dispersion force between two hexane molecules.

On the other hand, the ion-ion force is produced between ions of the same or different charge, where ions with charges of opposite sign attract each other and ions with charges of the same sign repel each other. This is the force that occurs between the NaCl ions.

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.