How many moles of nitrogen gas, n2, are there in 16.8 l of this gas at stp

  0.75 mol

Explanation:

- For any type of gas, the molar volume (the volume of one mole of     substance) at Standard Temperature and normal Pressure  is 22.4 L.

- Using cross multiplication,   1 mol    →   22.4 L

                                                        ?       →   16.8 L

So number of moles of N2 in 16.8 L  =  ( 16.8 L × 1 mol ) / 22.4 L = 0.75 mol ..

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6