Why does atomic size decrease as we move from left to right along a period in the periodic table?

Three elements $B$,$Si$ and $Ge$ are

Identify the elements with the following properties and arrange them in increasing order of their reactivity:
$(a)$ An element which is a soft and reactive metal.
$(b)$ The metal which is an important constituent of limestone.
$(c)$ The metal which exists in a liquid state at room temperature.

On moving from left to right in a period in the periodic table,the size of the atom.

$D$öbereiner's system of classification into triads was not found to be useful as he could identify only:

Write true or false for the statements: Non-metals are electronegative. They tend to form bonds by gaining electrons. As the trends in the electronegativity show,non-metals are found on the right-hand side of the periodic table towards the top.