Zinc + Hydrochloric Acid - Zinc Chloride and Hydrogen Gas Zn + 2HCI - ZnCl2 + Hz
I know there are 2 atoms of hydrogen in the products because there is

O a 2 in front of hydrochloric acid
O a 2 behind HCI
O a 2 behind H

O a 2 in front of hydrochloric acid

Explanation:

the given reaction is :-

=》Zn + 2 HCL -> ZnCl2 + H2

since, mass can't be created or destroy, so number of hydrogen atoms in the reaction should be equal in product as in reaction.

so, there is 2 hydrogen in product hence there are two hydrogen in the reactants also.

it is showed in the reaction by putting a 2 in front of hydrochloric acid ( HCl ).

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

elements make up everything, and they combine to make compounds.

the answer is c