Properties of elements in the periodic table:
The periodic table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configuration, and recurring chemical properties. It is divided into periods (horizontal rows) and groups (vertical columns). Different properties of elements can be observed as we move across periods and down groups in the periodic table.

Atomic Radius:
The atomic radius refers to the size of an atom, which is determined by the distance between the nucleus and the outermost electron shell. The atomic radius generally decreases from left to right across a period and increases from top to bottom within a group. This is because, as we move across a period, the number of protons in the nucleus increases, resulting in a stronger attractive force on the electrons and a smaller atomic radius. On the other hand, as we move down a group, additional electron shells are added, leading to an increase in atomic size.

Electronegativity:
Electronegativity is a measure of an atom's ability to attract shared electrons towards itself in a chemical bond. It also follows a similar trend to atomic radius. Electronegativity generally increases from left to right across a period and decreases from top to bottom within a group. This is because when moving across a period, the effective nuclear charge increases, making the atom more attractive to electrons. Conversely, as we move down a group, the increase in atomic size leads to a decrease in electronegativity.

Ionization Energy:
Ionization energy is the energy required to remove an electron from an atom, forming a positive ion. Similar to atomic radius and electronegativity, ionization energy exhibits a trend across periods and groups. Ionization energy generally increases from left to right across a period and decreases from top to bottom within a group. As we move across a period, the atomic radius decreases, resulting in a stronger attractive force on the outermost electrons, making it more difficult to remove them. Conversely, as we move down a group, the increase in atomic size reduces the effective nuclear charge, making it easier to remove electrons.

Metallic Character:
Metallic character refers to the extent to which an element exhibits the properties of a metal. It decreases from left to right across a period and increases from top to bottom within a group. Metals are generally found on the left side of the periodic table, and as we move across a period, the atomic radius decreases, resulting in a decrease in metallic character. On the other hand, as we move down a group, the increase in atomic size and the addition of electron shells lead to an increase in metallic character.

Conclusion:
In summary, the atomic radius, ionization energy, and metallic character decrease from left to right across the periodic table and increase from top to bottom within a group. Electronegativity follows a similar trend to atomic radius but in the opposite direction. Therefore, the correct answer is option 'D' (I and IV).