As astronomical telescope of ten fold angular magnification has a length of 44 cm. The focal length of the objective is:

40 cm

The correct answer is Option (2) → 40 cm

Magnification, $M=\frac{f_{objective}}{f_{eyepiece}}=10$

$⇒f_0=10f_e$

Length of the telescope, $L=f_0+f_e$

$⇒44=f_0+f_e$

$⇒44=10f_e+f_e$

$⇒f_e=4cm$

$∴f_0=f_e×10=4×10$

$=40cm$