Answer:
Explanation: Mendeleev arranged the elements on the basis of their atomic mass. Melting and boiling point were used as the physical characteristics in deciding the position of elements. He arranged the elements and wrote the formula of their oxides and hydrides which seemed to possess same chemical formula.
Explanation:
Formula units in 450 g of 
is 1.93 × 10²⁴ formula units.
<u>Explanation:</u>
First we have to find the number of moles in the given mass by dividing the mass by its molar mass as,
Now, we have to multiply the number of moles of Na₂SO₄ by the Avogadro's number, 6.022 × 10²³ formula units/mol, so we will get the number of formula units present in the given mass of the compound.
3.2 mol × 6.022 × 10²³ = 1.93 × 10²⁴ formula units.
So, 1.93 × 10²⁴ formula units is present in 450g of Na₂SO₄.
Blood.
<span>Blood is heterogeneous because it has corpuscles (blood cells and platelets) physically suspended in blood plasma. Blood plasma and the corpuscles have different properties and can be separated by methods such as centrifugation. Also, blood is considered a colloid suspension because it has the properties of both a colloid and a suspension. This is because the blood plasma acts as a colloid. More so, if blood was left to settle,then the blood cells would collect at the bottom hence taking the characteristic of a suspension. </span>
<span>Salad dressing.</span>
<span>Depending on the type of salad, it can either be a heterogeneous or homogeneous mixture. If the salad dressing is only of vinegar or any other oil, then it is a homogenous mixture. However, if it involves a mixture of vinegar and other oils, pepper, herbs, and etcetera, then it is a heterogeneous mixture</span>
The arrows represent the movement of starting substances
