What is the trend of valency along the periods in the modern periodic table?

it increases and then decreases

The correct answer is option 3. it increases and then decreases.

The valency of elements in the first group (Group 1, also known as alkali metals) is typically +1, as these elements readily lose one electron to achieve a stable electron configuration.

As you move across a period from left to right in the periodic table, the atomic number increases, and the number of valence electrons increases by one with each successive element. This generally leads to an increase in valency until you reach elements with a valency of 4 in the middle of the period, such as carbon (C) and silicon (Si), which can form four bonds due to having four valence electrons.

However, after reaching a peak, the valency starts to decrease as you continue moving to the right of the periodic table. Elements on the right side of the period (towards the noble gases) tend to have higher valency due to their tendency to gain electrons and achieve a stable electron configuration. For example, elements in Group 4A (Group 14) have a valency of 4, while those in Group 5A (Group 15) have a valency of 3, and so on.

So, indeed, the trend of valency generally increases from left to right until it reaches a maximum (often around 4) and then decreases.