Volume of body = 100 cm3
Weight of the body in air (W1) = 1 kgf = 1000 gf
Let the weight of the body in water be W2
Density = Mass\over Volume
= 1000\over 100 = 10 g cm-3
RD of body = 10\over 1 = 10
Now, RD of the body = W_1\over W_1 - W_2
⇒ 10 = 1000\over 1000 - W_2
⇒ 10 (1000 – W2) = 1000
⇒ 1000 – W2 = 100
⇒ W2 = 1000 – 100 = 900 gf
Hence,
(i) Weight in water = 900 gf
(ii) Relative density of body = 10