Which of these is a mixture? a) milk b) salt c) sulfuric acid d) carbon dioxide

A, milk. the rest are compounds

Explanation:

The correct answer is A . MIlk is a mixture because pure substances were combined together without formation of bonds, hence it would be easy to separate the substances. On the other hand, salt, sulfuric acid and carbon-dioxide are made from bonding between elements in the periodic table to form compounds. Salt is formed through bonding between Na and Cl atoms, while sulfuric acid is  made from bonding and ions. Carbon-dioxide is made from bonding between C and O elements. Compounds bond at a specific ratio while mixtures have no specific ratio of mixing.

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.