Question

cohesion occurs when __. to stick to surfaces like trees, geckos use __.
o two different substances stick together; adhesion
o two molecules of the same substance stick together; cohesion
o two molecules of the same substance stick together; adhesion
o two different substances stick together; cohesion

Explanation:

To solve this, we recall the definitions of cohesion and adhesion. Cohesion is the attraction between molecules of the same substance (they "stick together"). Adhesion is the attraction between molecules of different substances (or a substance and a surface).

Looking at the options for the first blank (cohesion):

• Option 1: Talks about different substances, which is adhesion, not cohesion. Eliminate.
• Option 2: Talks about same substance but labels it adhesion (wrong, adhesion is different substances). Eliminate.
• Option 3: Says two molecules of the same substance stick together, which matches cohesion's definition.
• Option 4: Talks about different substances for cohesion (wrong, cohesion is same substance). Eliminate.

For the second blank (to stick to surfaces like trees, geckos use...), adhesion is the attraction to surfaces (different from the gecko's foot substance, likely), so adhesion. But focusing on the first part for the cohesion definition, the correct option for the first blank (cohesion occurs when...) is the third option: "two molecules of the same substance stick together; cohesion". Wait, no, let's re - check. Wait, the first part is "Cohesion occurs when...". Cohesion is intra - molecular attraction (same substance). So:

• Option 1: two different substances stick together (that's adhesion), so wrong.
• Option 2: two molecules of same substance stick together but calls it adhesion (adhesion is inter - substance), wrong.
• Option 3: two molecules of same substance stick together; cohesion (correct, as cohesion is same - substance attraction).
• Option 4: two different substances stick together; cohesion (wrong, cohesion is same substance).

So the correct option for the first part (cohesion occurs when) is the third option: "two molecules of the same substance stick together; cohesion". But wait, the second part about geckos: geckos use adhesion to stick to surfaces (since their feet and the surface are different substances). But the question's first blank is about cohesion. So the correct option for the first blank (the cohesion part) is the third option.

Answer:

C. two molecules of the same substance stick together; cohesion (assuming the options are labeled A, B, C, D with A being the first option, B the second, C the third, D the fourth)