c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.
FOR 1ST QUESTION WE GO BY RATIO OF Z/E
AND IONIC SIZE IS INVERSLY PROPORTIONAL TO Z/E
SO WHOSE Z/E IS less WILL BE BIGGER
AND WHOSE Z/E IS MORE WILL BE SMALLER
(Z=atomic no )(e=no. of electrons in the ion )
In second question OPTION IS A
because size of inert gases are greatest in their respective period
in third again go for z/e ratio and you will get the answer .