The pair(s) of diamagnetic ions is(are)

For the reaction sequence given below, the correct statement(s) is(are)

(In the options, X is any atom other than carbon and hydrogen, and it is different in P, Q and R)

In an electrochemical cell, dichromate ions in aqueous acidic medium are reduced to Cr³⁺. The current (in amperes) that flows through the cell for 48.25 minutes to produce 1 mole of Cr³⁺ is ______.

Use: 1 Faraday = 96500 C mol⁻¹

At 25 °C, the concentration of H⁺ ions in 1.00 × 10⁻³ M aqueous solution of a weak monobasic acid having acid dissociation constant (K_a) of 4.00 × 10⁻¹¹ is X × 10⁻⁷ M. The value of X is ______.

Use: Ionic product of water (K_w) = 1.00 × 10⁻¹⁴ at 25 °C