The thin prism having refracting angle 10^ ^ is made of glass of...

For a thin prism, the deviation produced is given by $\delta = (\mu - 1)A$.

For the combination to produce dispersion without deviation, the net deviation must be zero. This means the deviations produced by the two prisms must be equal in magnitude and opposite in direction.

$(\mu_1 - 1)A_1 = (\mu_2 - 1)A_2$

Substituting the given values:

(1.42 - 1) \times 10^{}^{\circ} = (1.7 - 1) \times A_2

0.42 \times 10^{}^{\circ} = 0.7 \times A_2

4.2^{}^{\circ} = 0.7 A_2

A_2 = \dfrac{4.2^{}^{\circ}}{0.7} = 6^{}^{\circ}

Answer: 6^{}^{\circ}