The elements with atomic number 39 to 48 belong to:A.Fourth periodB.Fifth periodC.Sixth periodD.Third period

To determine which period the elements with atomic numbers 39 to 48 belong to, we first need to understand the structure of the periodic table and what "period" means.

Explanation of Periods
The periods in the periodic table represent the rows. Each period corresponds to the highest energy level of electrons in the atoms of the elements in that row.
The elements are arranged in order of increasing atomic number, which is the number of protons in the nucleus of an atom.
Elements with Atomic Numbers 39 to 48
Atomic number 39: Yttrium (Y)
Atomic number 40: Zirconium (Zr)
Atomic number 41: Niobium (Nb)
Atomic number 42: Molybdenum (Mo)
Atomic number 43: Technetium (Tc)
Atomic number 44: Ruthenium (Ru)
Atomic number 45: Rhodium (Rh)
Atomic number 46: Palladium (Pd)
Atomic number 47: Silver (Ag)
Atomic number 48: Cadmium (Cd)
Identifying the Period
The elements from atomic number 39 (Y) to atomic number 48 (Cd) are located in the fifth period of the periodic table.
This can be verified by checking the rows in the periodic table. The fifth period contains the elements from atomic numbers 37 (Rubidium, Rb) to 48 (Cadmium, Cd).
Conclusion
Thus, the elements with atomic numbers 39 to 48 belong to:

B. Fifth period