Ionic compounds are formed between oppositely charged ions.
A binary ionic compound is composed of ions of two different elements - one of which is a positive ion(metal), and the other is negative ion (nonmetal).
To write the empirical formula of binary ionic compound we must remember that one ion should be positive and other ion should be negative, then only the correct formula should be written. To write the empirical formula the charges of opposite ions should be criss-crossed.
First empirical formula of binary ionic compound is written between
First Formula would be 
Second empirical formula is between 
Second Formula would be 
Note : When the subscript are same they get cancel out, so 
would be written as 
Third empirical formula is between 
Third Formula would be :
Forth empirical formula is between 
Forth Formula would be : 
or 
Note- The subscript will be simplified and the formula will be written as .
The empirical formula of four binary ionic compounds are : 
A converging lens made from a transparent plastic bottle filled with water is used to enable Pak Dollah read the newspaper.
<h3>What is long-sightedness?</h3>
Long-sightedness is an eye effect in which objects are not able to focus on the retina but behind the retina, therefore, near objects are not clearly seen except they are placed far away.
To correct long-sightedness, a suitable converging lens is used to bring the image to focus on the retina.
To construct a converging lens for Pak Dollah, the transparent plastic bottle is filled with water to serve as a converging lens and Pal Dollah will read through it.
Therefore, a converging lens made from a transparent plastic bottle filled with water is used to enable Pak Dollah read the newspaper.
Learn more about long-sightedness at:brainly.com/question/4419161
Explanation:
As it is known that in solids, molecules are held together because of strong intermolecular forces of attraction. As a result, they are held together and have definite shape and volume.
Whereas in liquids, molecules are not held so strongly as they are in solids. Hence, they move from their initial position and they do not have definite shape but they have definite volume.
Liquids obtain the shape of container in which they are kept.
In gases, molecules are held together by weak intermolecular forces. As a result, they move far apart from each other and occupy the space of a container or vessel in which they are placed.
The physical state (at room temperature) of the following are determined as follows:
(a) Helium in a toy balloon : Helium at room temperature exists as a gas. So, when helium is present in a toy balloon then it acquires the volume of toy balloon.
(b) Mercury in a thermometer : Mercury at room temperature exists as a liquid. When it is placed in a thermometer then volume of mercury does not get affected.
(c) Soup in a bowl : Since, soup is a liquid. Hence, its volume will not change according to the volume of container.
