A sample of hydrogen gas, H2(g), is placed in a 0.500 L container at 295 K. The gas pressure is
1.442 bar.

pV=nRT

T = 295 K

V = 0.5 L = 0.5*10-3 m3

p = 1.442 bar = 144200 Pa

R = 8.314 J/mol*K

n = pV/RT = (144200*0.5*10-3)/(8.314*295) = 0,029 mol.

Explanation:

I know this because I just learned this in class

- 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