The isotope of an atom containing 31 protons and 39 neutrons suddenly has two neutrons added to it. What isotope is created?
Yttrium-72

Gallium-72

Gallium-41

Yttrium-41

Gallium-72

Explanation:

The elements are identified by the number of protons of the atom, which is its atomic number.

In this case the number of protons 39 (atomic number 39) permit you to identify the element as gallium.

Now, to identify the isotope you tell the name of the element and add the mass number.

The mass number is the sum of the protons and the neutrons

In this case, the number of neutrons is the original 39 plus the 2 added suddenly, i.e. 39 + 2 = 41, so the mass number is 31 + 41 = 72

Therefore, the isotope is gallium - 72.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements

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.