Which statement accurately compares the trends in atomic number and atomic mass in the periodic table?

valency in the periodic table across a period first increases and then decreases. there is no change going down a group. however, this periodic trend is sparsely followed for heavier elements (elements with atomic number greater than 20), especially for lanthanide and actinide series.

explanation:

periodic trends, or periodicity, appear with remarkable accuracy for many physical and chemical properties. the size, mass, reactivity and other atomic properties have few exceptions as you move from left to right and top to bottom on the modern periodic table.   shells closer to the nucleus—those with a smaller radius—are generally filled first, since the negatively charged electrons are attracted by the positively charged protons in the nucleus. as the atomic number increases along a row of the periodic table, additional electrons are added to the same, outermost shell.

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while it was true that the cotton gin reduced the labor of removing seeds, it did not reduce the need for slaves to grow and pick the cotton.

explanation:

before eli whitney's invention of the cotton gin, picking and cleaning cotton was a slow, labor-intensive job. workers, usually slaves, had to pick the seeds from the cotton fibers by hand. this invention made it possible to grow large amounts of cotton on big farms and make money.