Only cash contributions (e.g., checks, credit card charges) are acceptable in 529 plans. You’ll have to sell the stock and donate the proceeds. If the stock has appreciated, you’ll owe capital gains tax on your profits; if the value has declined, you’ll be able to take a tax loss.
Advance payment of current tax liability based either on wage withholdings or installment payments of your estimated tax liability. To avoid penalties, you generally must pay to the IRS either 90% of your final tax liability, or either 100% or 110% of the prior year’s tax liability, depending on your adjusted gross income.