The students in mr. black's class are studying about gases and earth's atmosphere. mr. black placed a deflated soccer ball on the balance. the balance read 560 grams. next mr. black took out a bicycle pump and pumped the soccer ball up until it was nice and round. he put the ball back on the balance and read 570 grams! with this experiment, mr. black just showed his students that air a) has mass. b) has weight. c) takes up space. d) is made up of oxygen and nitrogen.

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms

im not exactly sure but i think its b!