The correct option is B (3), (4) and (6)
(1) Sales of Rs. 950 to Ram completely omitted from books of account- Complete omission, no effect on the trial balance.
(2) Purchases of Rs. 720 from Shyam entered in the purchases journal as Rs. 700- Original entry with the wrong amount. Double-sided error, hence no effect on the trial balance.
(3) Purchases Journal is overcast by Rs. 1,000- It's an error of commission. Single-sided error, hence trial balance will have a difference.
(4) Sales returns journal is undercast by Rs. 200- It's an error of commission. Single-sided error, hence trial balance will have a difference.
(5) Amount paid to Agarwal wrongly posted to the debit to Mina's account- It's an error of posting in the wrong account. Hence no effect on the trial balance.
(6) Bank overdraft shown under debit column in the Trial Balance- Bank o/d always have a credit balance. This will affect the trial balance.
(7) Sales of Rs. 500 to Sadiq entered in sales journal as sales to Mushtaq- It's an error of posting in the wrong account, hence no effect on the trial balance.
(8) Wages paid for the installation of machinery debited to wages account- It's an error of principle. It does not have any effect on the trial balance.