H₂/Pd, LiAlH₄ and NaBH₄ are used to convert RCHO into RCH₂OH.

Aldehydes can be converted to their corresponding alcohols by Hydrogen in the presence of a catalyst such as Pd, Pt or Ni.

Aldehydes can be converted to their corresponding primary alcohols by Lithium aluminium hydride or Sodium borohydride.

Hence, options (i), (ii) and (iii) are correct.

Option (iv) is incorrect because reaction of RCHO with RMgX followed by hydrolysis, results in the formation of secondary alcohol.