Order the following in terms of decreasing atomic radius:

Ba, Cs, Hf, Bi, Ta

Cs > Ba > Bi > Hf > Ta

Explanation:

The atomic radius of a chemical element defined as the distance between nucleus and electron from the center.

The atomic number and atomic radius of given elements are:

Barium (Ba):

Atomic number - (56)

Atomic radius -  268 pm

Caesium (Cs)

Atomic number - 55

Atomic radius -  343 pm

Hafnium (Hf):

Atomic number - 72

Atomic radius -  225 pm

Bismuth (Bi):

Atomic number - 83

Atomic radius -  230

Tantalum (Ta):

Atomic number - 73

Atomic radius -  220 pm

According to the given atomic radius the decreasing order of atomic radius is Cs > Ba > Bi > Hf > Ta.

Caesium has highest atomic radius among all even though lowest atomic number because the force of attraction between the nucleus and the outermost electron is low and outermost electron are loosely held.

Barium (Ba) has lower atomic number than Bismuth (Bi) but still atomic radius of Barium is high because moving across the periodic table atomic radius decreases as force of attraction between nucleus and outer electrons is high.

Bismuth (Bi) has higher atomic number that Hafnium (Hf), atomic radius of Bi is more than Hf.

Tantalum (Ta) have higher atomic number than Hafnium (Hf) but still have lower atomic radius as as force of attraction between nucleus and outer electrons is high.

Hence, the decreasing atomic radius is Cs > Ba > Bi > Hf > Ta.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.