What is the formula of the ionic compound expected to form between the elements f and ca?

Ionic compounds are compounds made up of elements in which one has the tendency to loose electrons whereas the other has the tendency to gain electrons. Loss of electron results in the formation of a positively charged ion (cation) while gain of electrons results in the formation of negatively charged ions (anions). Usually metals have the tendency to loose electrons and non-metals tend to gain electrons.

Calcium (Ca) is a metal and belongs to group IIA in the periodic table with a valence electron configuration of 4s2

Fluorine (F) is a non-metal and belongs to group VIIA in the periodic table with a valence configuration of 2s22p5.

Thus, Ca will donate its outer 2 electrons to F, thus allowing each of the electronegative F atoms to complete its octet.

Therefore, we have:

Ca2+   +    F-           CaF2

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

explanation:

venn diagram is pictorial representation with of circles showing the relation between two finite sets or things. the intersection part of two circles conveys the relation present in between those sets or things.

here in the venn diagram of sand and salt two circles represent sand and salt. but the area falling under the intersection of these circle represents the mixture of sand and salt.

so, in a venn diagram the mixture will be placed in a middle that is in between the intersection of two circles.