if 3.5 g of element x reacts with 10.5 g of element y to form the compound xy.
what is the percent by mass of element x in the compound? the percent by mass
of element y?

The percentage by mass of element X is 25 %.

The percentage by mass of element Y is 75 %

Explanation:

X + Y ⇒ XY

3.5 g of element X + 10.5 g of element Y = 14g in total

⇒Element X : 3.5g / 14g = 0.25 ⇒ x 100 % = 25 %

⇒Element Y : 10.5 / 14 = 0.75 ⇒ x 100 % = 75 %

The percentage by mass of element X is 25 %.

The percentage by mass of element Y is 75 %

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.