Well, an element is a substance that cannot be decomposed into a simpler substance by chemical change, so element is the answer you are probably looking for! Hope this helps!
Answer:
Mass cannot be created or destroyed
Explanation:
The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.
Answer:

Explanation:
Half reaction:
(1)
balance: 
(2)H and O balance in acidic medium:
(3) charge balance:
Hence balanced half-reaction:
Answer:
Hg(NO₃)₂(aq) + Na₂SO₄(aq) → 2NaNO₃(aq) + HgSO₄(s)
Moles of Hg(NO₃)₂ = 55.42 / 324.7 ==> 0.1707 moles
Moles of Na₂SO₄ = 16.642 / 142.04 ==> 0.1172 moles
Limiting reagent is Na₂SO₄ as it controls product formation
Moles of HgSO₄ formed = 0.1172 moles
= 0.1172 x 296.65
= 34.757g
Explanation:
The answer should be A, increase the concentration of both