Questions

While moving from left to right in periodic table basic character of oxide of elements will decrease.

  ∴→Increasing basic strengthAl2O3<MgO<Na2O 

and while descending in the group basic character of corresponding oxides increases. 

 ∴→Increasing basic strengthNa2O<K2O

∴ Correct Order is Al2O3 < MgO <Na2O <K2O

A pure substance can be defined as any single type of material that has not been contaminated by another substance. In chemistry, a pure substance has a definite composition. It can be a compound or an element. A pure substance is considered to be a material that consists of one type of "building block" of matter.

Examples of pure substances include tin, sulfur, diamond, water, pure sugar (sucrose), table salt (sodium chloride) and baking soda (sodium bicarbonate).

Tin, sulfur, and diamond are examples of pure substances which are chemical elements. All elements are pure substances.

Water, sugar, salt and baking soda are pure substances which are chemical compounds. Chemical compounds also are pure substances

Yes, when rain starts falling umbrella goes up for pretecting us from wetting.

2+2=4

4+4=8

8+8=16

16+16=32 but  it is given 36

Although it is less accurate than adding up individual costs from the WBS, it is less time consuming. The trade-off is accuracy. Answer A is incorrect because to do a more accurate cost estimate, you need to delve into details. Answer C is tempting also, and possible, except we don't really know if the project in question can use perametric modeling . Answer D is incorrect because it takes the most time, but it is most accurate.